2 @c This is part of the GNU Guile Reference Manual.
3 @c Copyright (C) 1996, 1997, 2000, 2001, 2002, 2003, 2004, 2007, 2009,
4 @c 2010, 2011, 2013 Free Software Foundation, Inc.
5 @c See the file guile.texi for copying conditions.
8 @section Input and Output
11 * Ports:: The idea of the port abstraction.
12 * Reading:: Procedures for reading from a port.
13 * Writing:: Procedures for writing to a port.
14 * Closing:: Procedures to close a port.
15 * Random Access:: Moving around a random access port.
16 * Line/Delimited:: Read and write lines or delimited text.
17 * Block Reading and Writing:: Reading and writing blocks of text.
18 * Default Ports:: Defaults for input, output and errors.
19 * Port Types:: Types of port and how to make them.
20 * R6RS I/O Ports:: The R6RS port API.
21 * I/O Extensions:: Using and extending ports in C.
22 * BOM Handling:: Handling of Unicode byte order marks.
30 Sequential input/output in Scheme is represented by operations on a
31 @dfn{port}. This chapter explains the operations that Guile provides
32 for working with ports.
34 Ports are created by opening, for instance @code{open-file} for a file
35 (@pxref{File Ports}). Characters can be read from an input port and
36 written to an output port, or both on an input/output port. A port
37 can be closed (@pxref{Closing}) when no longer required, after which
38 any attempt to read or write is an error.
40 The formal definition of a port is very generic: an input port is
41 simply ``an object which can deliver characters on demand,'' and an
42 output port is ``an object which can accept characters.'' Because
43 this definition is so loose, it is easy to write functions that
44 simulate ports in software. @dfn{Soft ports} and @dfn{string ports}
45 are two interesting and powerful examples of this technique.
46 (@pxref{Soft Ports}, and @ref{String Ports}.)
48 Ports are garbage collected in the usual way (@pxref{Memory
49 Management}), and will be closed at that time if not already closed.
50 In this case any errors occurring in the close will not be reported.
51 Usually a program will want to explicitly close so as to be sure all
52 its operations have been successful. Of course if a program has
53 abandoned something due to an error or other condition then closing
54 problems are probably not of interest.
56 It is strongly recommended that file ports be closed explicitly when
57 no longer required. Most systems have limits on how many files can be
58 open, both on a per-process and a system-wide basis. A program that
59 uses many files should take care not to hit those limits. The same
60 applies to similar system resources such as pipes and sockets.
62 Note that automatic garbage collection is triggered only by memory
63 consumption, not by file or other resource usage, so a program cannot
64 rely on that to keep it away from system limits. An explicit call to
65 @code{gc} can of course be relied on to pick up unreferenced ports.
66 If program flow makes it hard to be certain when to close then this
67 may be an acceptable way to control resource usage.
69 All file access uses the ``LFS'' large file support functions when
70 available, so files bigger than 2 Gbytes (@math{2^31} bytes) can be
71 read and written on a 32-bit system.
73 Each port has an associated character encoding that controls how bytes
74 read from the port are converted to characters and string and controls
75 how characters and strings written to the port are converted to bytes.
76 When ports are created, they inherit their character encoding from the
77 current locale, but, that can be modified after the port is created.
79 Currently, the ports only work with @emph{non-modal} encodings. Most
80 encodings are non-modal, meaning that the conversion of bytes to a
81 string doesn't depend on its context: the same byte sequence will always
82 return the same string. A couple of modal encodings are in common use,
83 like ISO-2022-JP and ISO-2022-KR, and they are not yet supported.
85 Each port also has an associated conversion strategy: what to do when
86 a Guile character can't be converted to the port's encoded character
87 representation for output. There are three possible strategies: to
88 raise an error, to replace the character with a hex escape, or to
89 replace the character with a substitute character.
92 @deffn {Scheme Procedure} input-port? x
93 @deffnx {C Function} scm_input_port_p (x)
94 Return @code{#t} if @var{x} is an input port, otherwise return
95 @code{#f}. Any object satisfying this predicate also satisfies
100 @deffn {Scheme Procedure} output-port? x
101 @deffnx {C Function} scm_output_port_p (x)
102 Return @code{#t} if @var{x} is an output port, otherwise return
103 @code{#f}. Any object satisfying this predicate also satisfies
107 @deffn {Scheme Procedure} port? x
108 @deffnx {C Function} scm_port_p (x)
109 Return a boolean indicating whether @var{x} is a port.
110 Equivalent to @code{(or (input-port? @var{x}) (output-port?
114 @deffn {Scheme Procedure} set-port-encoding! port enc
115 @deffnx {C Function} scm_set_port_encoding_x (port, enc)
116 Sets the character encoding that will be used to interpret all port I/O.
117 @var{enc} is a string containing the name of an encoding. Valid
118 encoding names are those
119 @url{http://www.iana.org/assignments/character-sets, defined by IANA}.
122 @defvr {Scheme Variable} %default-port-encoding
123 A fluid containing @code{#f} or the name of the encoding to
124 be used by default for newly created ports (@pxref{Fluids and Dynamic
125 States}). The value @code{#f} is equivalent to @code{"ISO-8859-1"}.
127 New ports are created with the encoding appropriate for the current
128 locale if @code{setlocale} has been called or the value specified by
129 this fluid otherwise.
132 @deffn {Scheme Procedure} port-encoding port
133 @deffnx {C Function} scm_port_encoding (port)
134 Returns, as a string, the character encoding that @var{port} uses to interpret
135 its input and output. The value @code{#f} is equivalent to @code{"ISO-8859-1"}.
138 @deffn {Scheme Procedure} set-port-conversion-strategy! port sym
139 @deffnx {C Function} scm_set_port_conversion_strategy_x (port, sym)
140 Sets the behavior of the interpreter when outputting a character that
141 is not representable in the port's current encoding. @var{sym} can be
142 either @code{'error}, @code{'substitute}, or @code{'escape}. If it is
143 @code{'error}, an error will be thrown when an nonconvertible character
144 is encountered. If it is @code{'substitute}, then nonconvertible
145 characters will be replaced with approximate characters, or with
146 question marks if no approximately correct character is available. If
147 it is @code{'escape}, it will appear as a hex escape when output.
149 If @var{port} is an open port, the conversion error behavior
150 is set for that port. If it is @code{#f}, it is set as the
151 default behavior for any future ports that get created in
155 @deffn {Scheme Procedure} port-conversion-strategy port
156 @deffnx {C Function} scm_port_conversion_strategy (port)
157 Returns the behavior of the port when outputting a character that is
158 not representable in the port's current encoding. It returns the
159 symbol @code{error} if unrepresentable characters should cause
160 exceptions, @code{substitute} if the port should try to replace
161 unrepresentable characters with question marks or approximate
162 characters, or @code{escape} if unrepresentable characters should be
163 converted to string escapes.
165 If @var{port} is @code{#f}, then the current default behavior will be
166 returned. New ports will have this default behavior when they are
170 @deffn {Scheme Variable} %default-port-conversion-strategy
171 The fluid that defines the conversion strategy for newly created ports,
172 and for other conversion routines such as @code{scm_to_stringn},
173 @code{scm_from_stringn}, @code{string->pointer}, and
174 @code{pointer->string}.
176 Its value must be one of the symbols described above, with the same
177 semantics: @code{'error}, @code{'substitute}, or @code{'escape}.
179 When Guile starts, its value is @code{'substitute}.
181 Note that @code{(set-port-conversion-strategy! #f @var{sym})} is
182 equivalent to @code{(fluid-set! %default-port-conversion-strategy
191 [Generic procedures for reading from ports.]
193 These procedures pertain to reading characters and strings from
194 ports. To read general S-expressions from ports, @xref{Scheme Read}.
197 @cindex End of file object
198 @deffn {Scheme Procedure} eof-object? x
199 @deffnx {C Function} scm_eof_object_p (x)
200 Return @code{#t} if @var{x} is an end-of-file object; otherwise
205 @deffn {Scheme Procedure} char-ready? [port]
206 @deffnx {C Function} scm_char_ready_p (port)
207 Return @code{#t} if a character is ready on input @var{port}
208 and return @code{#f} otherwise. If @code{char-ready?} returns
209 @code{#t} then the next @code{read-char} operation on
210 @var{port} is guaranteed not to hang. If @var{port} is a file
211 port at end of file then @code{char-ready?} returns @code{#t}.
213 @code{char-ready?} exists to make it possible for a
214 program to accept characters from interactive ports without
215 getting stuck waiting for input. Any input editors associated
216 with such ports must make sure that characters whose existence
217 has been asserted by @code{char-ready?} cannot be rubbed out.
218 If @code{char-ready?} were to return @code{#f} at end of file,
219 a port at end of file would be indistinguishable from an
220 interactive port that has no ready characters.
224 @deffn {Scheme Procedure} read-char [port]
225 @deffnx {C Function} scm_read_char (port)
226 Return the next character available from @var{port}, updating
227 @var{port} to point to the following character. If no more
228 characters are available, the end-of-file object is returned.
230 When @var{port}'s data cannot be decoded according to its
231 character encoding, a @code{decoding-error} is raised and
232 @var{port} points past the erroneous byte sequence.
235 @deftypefn {C Function} size_t scm_c_read (SCM port, void *buffer, size_t size)
236 Read up to @var{size} bytes from @var{port} and store them in
237 @var{buffer}. The return value is the number of bytes actually read,
238 which can be less than @var{size} if end-of-file has been reached.
240 Note that this function does not update @code{port-line} and
241 @code{port-column} below.
245 @deffn {Scheme Procedure} peek-char [port]
246 @deffnx {C Function} scm_peek_char (port)
247 Return the next character available from @var{port},
248 @emph{without} updating @var{port} to point to the following
249 character. If no more characters are available, the
250 end-of-file object is returned.
252 The value returned by
253 a call to @code{peek-char} is the same as the value that would
254 have been returned by a call to @code{read-char} on the same
255 port. The only difference is that the very next call to
256 @code{read-char} or @code{peek-char} on that @var{port} will
257 return the value returned by the preceding call to
258 @code{peek-char}. In particular, a call to @code{peek-char} on
259 an interactive port will hang waiting for input whenever a call
260 to @code{read-char} would have hung.
262 As for @code{read-char}, a @code{decoding-error} may be raised
263 if such a situation occurs. However, unlike with @code{read-char},
264 @var{port} still points at the beginning of the erroneous byte
265 sequence when the error is raised.
268 @deffn {Scheme Procedure} unread-char cobj [port]
269 @deffnx {C Function} scm_unread_char (cobj, port)
270 Place character @var{cobj} in @var{port} so that it will be read by the
271 next read operation. If called multiple times, the unread characters
272 will be read again in last-in first-out order. If @var{port} is
273 not supplied, the current input port is used.
276 @deffn {Scheme Procedure} unread-string str port
277 @deffnx {C Function} scm_unread_string (str, port)
278 Place the string @var{str} in @var{port} so that its characters will
279 be read from left-to-right as the next characters from @var{port}
280 during subsequent read operations. If called multiple times, the
281 unread characters will be read again in last-in first-out order. If
282 @var{port} is not supplied, the @code{current-input-port} is used.
285 @deffn {Scheme Procedure} drain-input port
286 @deffnx {C Function} scm_drain_input (port)
287 This procedure clears a port's input buffers, similar
288 to the way that force-output clears the output buffer. The
289 contents of the buffers are returned as a single string, e.g.,
292 (define p (open-input-file ...))
293 (drain-input p) => empty string, nothing buffered yet.
294 (unread-char (read-char p) p)
295 (drain-input p) => initial chars from p, up to the buffer size.
298 Draining the buffers may be useful for cleanly finishing
299 buffered I/O so that the file descriptor can be used directly
303 @deffn {Scheme Procedure} port-column port
304 @deffnx {Scheme Procedure} port-line port
305 @deffnx {C Function} scm_port_column (port)
306 @deffnx {C Function} scm_port_line (port)
307 Return the current column number or line number of @var{port}.
309 unknown, the result is #f. Otherwise, the result is a 0-origin integer
310 - i.e.@: the first character of the first line is line 0, column 0.
311 (However, when you display a file position, for example in an error
312 message, we recommend you add 1 to get 1-origin integers. This is
313 because lines and column numbers traditionally start with 1, and that is
314 what non-programmers will find most natural.)
317 @deffn {Scheme Procedure} set-port-column! port column
318 @deffnx {Scheme Procedure} set-port-line! port line
319 @deffnx {C Function} scm_set_port_column_x (port, column)
320 @deffnx {C Function} scm_set_port_line_x (port, line)
321 Set the current column or line number of @var{port}.
328 [Generic procedures for writing to ports.]
330 These procedures are for writing characters and strings to
331 ports. For more information on writing arbitrary Scheme objects to
332 ports, @xref{Scheme Write}.
334 @deffn {Scheme Procedure} get-print-state port
335 @deffnx {C Function} scm_get_print_state (port)
336 Return the print state of the port @var{port}. If @var{port}
337 has no associated print state, @code{#f} is returned.
341 @deffn {Scheme Procedure} newline [port]
342 @deffnx {C Function} scm_newline (port)
343 Send a newline to @var{port}.
344 If @var{port} is omitted, send to the current output port.
347 @deffn {Scheme Procedure} port-with-print-state port [pstate]
348 @deffnx {C Function} scm_port_with_print_state (port, pstate)
349 Create a new port which behaves like @var{port}, but with an
350 included print state @var{pstate}. @var{pstate} is optional.
351 If @var{pstate} isn't supplied and @var{port} already has
352 a print state, the old print state is reused.
355 @deffn {Scheme Procedure} simple-format destination message . args
356 @deffnx {C Function} scm_simple_format (destination, message, args)
357 Write @var{message} to @var{destination}, defaulting to
358 the current output port.
359 @var{message} can contain @code{~A} (was @code{%s}) and
360 @code{~S} (was @code{%S}) escapes. When printed,
361 the escapes are replaced with corresponding members of
363 @code{~A} formats using @code{display} and @code{~S} formats
365 If @var{destination} is @code{#t}, then use the current output
366 port, if @var{destination} is @code{#f}, then return a string
367 containing the formatted text. Does not add a trailing newline.
371 @deffn {Scheme Procedure} write-char chr [port]
372 @deffnx {C Function} scm_write_char (chr, port)
373 Send character @var{chr} to @var{port}.
376 @deftypefn {C Function} void scm_c_write (SCM port, const void *buffer, size_t size)
377 Write @var{size} bytes at @var{buffer} to @var{port}.
379 Note that this function does not update @code{port-line} and
380 @code{port-column} (@pxref{Reading}).
384 @deffn {Scheme Procedure} force-output [port]
385 @deffnx {C Function} scm_force_output (port)
386 Flush the specified output port, or the current output port if @var{port}
387 is omitted. The current output buffer contents are passed to the
388 underlying port implementation (e.g., in the case of fports, the
389 data will be written to the file and the output buffer will be cleared.)
390 It has no effect on an unbuffered port.
392 The return value is unspecified.
395 @deffn {Scheme Procedure} flush-all-ports
396 @deffnx {C Function} scm_flush_all_ports ()
397 Equivalent to calling @code{force-output} on
398 all open output ports. The return value is unspecified.
404 @cindex Closing ports
407 @deffn {Scheme Procedure} close-port port
408 @deffnx {C Function} scm_close_port (port)
409 Close the specified port object. Return @code{#t} if it
410 successfully closes a port or @code{#f} if it was already
411 closed. An exception may be raised if an error occurs, for
412 example when flushing buffered output. See also @ref{Ports and
413 File Descriptors, close}, for a procedure which can close file
417 @deffn {Scheme Procedure} close-input-port port
418 @deffnx {Scheme Procedure} close-output-port port
419 @deffnx {C Function} scm_close_input_port (port)
420 @deffnx {C Function} scm_close_output_port (port)
421 @rnindex close-input-port
422 @rnindex close-output-port
423 Close the specified input or output @var{port}. An exception may be
424 raised if an error occurs while closing. If @var{port} is already
425 closed, nothing is done. The return value is unspecified.
427 See also @ref{Ports and File Descriptors, close}, for a procedure
428 which can close file descriptors.
431 @deffn {Scheme Procedure} port-closed? port
432 @deffnx {C Function} scm_port_closed_p (port)
433 Return @code{#t} if @var{port} is closed or @code{#f} if it is
439 @subsection Random Access
440 @cindex Random access, ports
441 @cindex Port, random access
443 @deffn {Scheme Procedure} seek fd_port offset whence
444 @deffnx {C Function} scm_seek (fd_port, offset, whence)
445 Sets the current position of @var{fd_port} to the integer
446 @var{offset}, which is interpreted according to the value of
449 One of the following variables should be supplied for
452 Seek from the beginning of the file.
455 Seek from the current position.
458 Seek from the end of the file.
460 If @var{fd_port} is a file descriptor, the underlying system
461 call is @code{lseek}. @var{port} may be a string port.
463 The value returned is the new position in the file. This means
464 that the current position of a port can be obtained using:
466 (seek port 0 SEEK_CUR)
470 @deffn {Scheme Procedure} ftell fd_port
471 @deffnx {C Function} scm_ftell (fd_port)
472 Return an integer representing the current position of
473 @var{fd_port}, measured from the beginning. Equivalent to:
476 (seek port 0 SEEK_CUR)
482 @deffn {Scheme Procedure} truncate-file file [length]
483 @deffnx {C Function} scm_truncate_file (file, length)
484 Truncate @var{file} to @var{length} bytes. @var{file} can be a
485 filename string, a port object, or an integer file descriptor. The
486 return value is unspecified.
488 For a port or file descriptor @var{length} can be omitted, in which
489 case the file is truncated at the current position (per @code{ftell}
492 On most systems a file can be extended by giving a length greater than
493 the current size, but this is not mandatory in the POSIX standard.
497 @subsection Line Oriented and Delimited Text
498 @cindex Line input/output
499 @cindex Port, line input/output
501 The delimited-I/O module can be accessed with:
504 (use-modules (ice-9 rdelim))
507 It can be used to read or write lines of text, or read text delimited by
508 a specified set of characters. It's similar to the @code{(scsh rdelim)}
509 module from guile-scsh, but does not use multiple values or character
510 sets and has an extra procedure @code{write-line}.
512 @c begin (scm-doc-string "rdelim.scm" "read-line")
513 @deffn {Scheme Procedure} read-line [port] [handle-delim]
514 Return a line of text from @var{port} if specified, otherwise from the
515 value returned by @code{(current-input-port)}. Under Unix, a line of text
516 is terminated by the first end-of-line character or by end-of-file.
518 If @var{handle-delim} is specified, it should be one of the following
522 Discard the terminating delimiter. This is the default, but it will
523 be impossible to tell whether the read terminated with a delimiter or
526 Append the terminating delimiter (if any) to the returned string.
528 Push the terminating delimiter (if any) back on to the port.
530 Return a pair containing the string read from the port and the
531 terminating delimiter or end-of-file object.
534 Like @code{read-char}, this procedure can throw to @code{decoding-error}
535 (@pxref{Reading, @code{read-char}}).
538 @c begin (scm-doc-string "rdelim.scm" "read-line!")
539 @deffn {Scheme Procedure} read-line! buf [port]
540 Read a line of text into the supplied string @var{buf} and return the
541 number of characters added to @var{buf}. If @var{buf} is filled, then
542 @code{#f} is returned.
543 Read from @var{port} if
544 specified, otherwise from the value returned by @code{(current-input-port)}.
547 @c begin (scm-doc-string "rdelim.scm" "read-delimited")
548 @deffn {Scheme Procedure} read-delimited delims [port] [handle-delim]
549 Read text until one of the characters in the string @var{delims} is found
550 or end-of-file is reached. Read from @var{port} if supplied, otherwise
551 from the value returned by @code{(current-input-port)}.
552 @var{handle-delim} takes the same values as described for @code{read-line}.
555 @c begin (scm-doc-string "rdelim.scm" "read-delimited!")
556 @deffn {Scheme Procedure} read-delimited! delims buf [port] [handle-delim] [start] [end]
557 Read text into the supplied string @var{buf}.
559 If a delimiter was found, return the number of characters written,
560 except if @var{handle-delim} is @code{split}, in which case the return
561 value is a pair, as noted above.
563 As a special case, if @var{port} was already at end-of-stream, the EOF
564 object is returned. Also, if no characters were written because the
565 buffer was full, @code{#f} is returned.
567 It's something of a wacky interface, to be honest.
570 @deffn {Scheme Procedure} write-line obj [port]
571 @deffnx {C Function} scm_write_line (obj, port)
572 Display @var{obj} and a newline character to @var{port}. If
573 @var{port} is not specified, @code{(current-output-port)} is
574 used. This function is equivalent to:
581 In the past, Guile did not have a procedure that would just read out all
582 of the characters from a port. As a workaround, many people just called
583 @code{read-delimited} with no delimiters, knowing that would produce the
584 behavior they wanted. This prompted Guile developers to add some
585 routines that would read all characters from a port. So it is that
586 @code{(ice-9 rdelim)} is also the home for procedures that can reading
589 @deffn {Scheme Procedure} read-string [port] [count]
590 Read all of the characters out of @var{port} and return them as a
591 string. If the @var{count} is present, treat it as a limit to the
592 number of characters to read.
594 By default, read from the current input port, with no size limit on the
595 result. This procedure always returns a string, even if no characters
599 @deffn {Scheme Procedure} read-string! buf [port] [start] [end]
600 Fill @var{buf} with characters read from @var{port}, defaulting to the
601 current input port. Return the number of characters read.
603 If @var{start} or @var{end} are specified, store data only into the
604 substring of @var{str} bounded by @var{start} and @var{end} (which
605 default to the beginning and end of the string, respectively).
608 Some of the aforementioned I/O functions rely on the following C
609 primitives. These will mainly be of interest to people hacking Guile
612 @deffn {Scheme Procedure} %read-delimited! delims str gobble [port [start [end]]]
613 @deffnx {C Function} scm_read_delimited_x (delims, str, gobble, port, start, end)
614 Read characters from @var{port} into @var{str} until one of the
615 characters in the @var{delims} string is encountered. If
616 @var{gobble} is true, discard the delimiter character;
617 otherwise, leave it in the input stream for the next read. If
618 @var{port} is not specified, use the value of
619 @code{(current-input-port)}. If @var{start} or @var{end} are
620 specified, store data only into the substring of @var{str}
621 bounded by @var{start} and @var{end} (which default to the
622 beginning and end of the string, respectively).
624 Return a pair consisting of the delimiter that terminated the
625 string and the number of characters read. If reading stopped
626 at the end of file, the delimiter returned is the
627 @var{eof-object}; if the string was filled without encountering
628 a delimiter, this value is @code{#f}.
631 @deffn {Scheme Procedure} %read-line [port]
632 @deffnx {C Function} scm_read_line (port)
633 Read a newline-terminated line from @var{port}, allocating storage as
634 necessary. The newline terminator (if any) is removed from the string,
635 and a pair consisting of the line and its delimiter is returned. The
636 delimiter may be either a newline or the @var{eof-object}; if
637 @code{%read-line} is called at the end of file, it returns the pair
638 @code{(#<eof> . #<eof>)}.
641 @node Block Reading and Writing
642 @subsection Block reading and writing
643 @cindex Block read/write
644 @cindex Port, block read/write
646 The Block-string-I/O module can be accessed with:
649 (use-modules (ice-9 rw))
652 It currently contains procedures that help to implement the
653 @code{(scsh rw)} module in guile-scsh.
655 @deffn {Scheme Procedure} read-string!/partial str [port_or_fdes [start [end]]]
656 @deffnx {C Function} scm_read_string_x_partial (str, port_or_fdes, start, end)
657 Read characters from a port or file descriptor into a
658 string @var{str}. A port must have an underlying file
659 descriptor --- a so-called fport. This procedure is
660 scsh-compatible and can efficiently read large strings.
665 attempt to fill the entire string, unless the @var{start}
666 and/or @var{end} arguments are supplied. i.e., @var{start}
667 defaults to 0 and @var{end} defaults to
668 @code{(string-length str)}
670 use the current input port if @var{port_or_fdes} is not
673 return fewer than the requested number of characters in some
674 cases, e.g., on end of file, if interrupted by a signal, or if
675 not all the characters are immediately available.
677 wait indefinitely for some input if no characters are
679 unless the port is in non-blocking mode.
681 read characters from the port's input buffers if available,
682 instead from the underlying file descriptor.
684 return @code{#f} if end-of-file is encountered before reading
685 any characters, otherwise return the number of characters
688 return 0 if the port is in non-blocking mode and no characters
689 are immediately available.
691 return 0 if the request is for 0 bytes, with no
696 @deffn {Scheme Procedure} write-string/partial str [port_or_fdes [start [end]]]
697 @deffnx {C Function} scm_write_string_partial (str, port_or_fdes, start, end)
698 Write characters from a string @var{str} to a port or file
699 descriptor. A port must have an underlying file descriptor
700 --- a so-called fport. This procedure is
701 scsh-compatible and can efficiently write large strings.
706 attempt to write the entire string, unless the @var{start}
707 and/or @var{end} arguments are supplied. i.e., @var{start}
708 defaults to 0 and @var{end} defaults to
709 @code{(string-length str)}
711 use the current output port if @var{port_of_fdes} is not
714 in the case of a buffered port, store the characters in the
715 port's output buffer, if all will fit. If they will not fit
716 then any existing buffered characters will be flushed
718 to write the new characters directly to the underlying file
719 descriptor. If the port is in non-blocking mode and
720 buffered characters can not be flushed immediately, then an
721 @code{EAGAIN} system-error exception will be raised (Note:
722 scsh does not support the use of non-blocking buffered ports.)
724 write fewer than the requested number of
725 characters in some cases, e.g., if interrupted by a signal or
726 if not all of the output can be accepted immediately.
728 wait indefinitely for at least one character
729 from @var{str} to be accepted by the port, unless the port is
730 in non-blocking mode.
732 return the number of characters accepted by the port.
734 return 0 if the port is in non-blocking mode and can not accept
735 at least one character from @var{str} immediately
737 return 0 immediately if the request size is 0 bytes.
742 @subsection Default Ports for Input, Output and Errors
743 @cindex Default ports
744 @cindex Port, default
746 @rnindex current-input-port
747 @deffn {Scheme Procedure} current-input-port
748 @deffnx {C Function} scm_current_input_port ()
749 @cindex standard input
750 Return the current input port. This is the default port used
751 by many input procedures.
753 Initially this is the @dfn{standard input} in Unix and C terminology.
754 When the standard input is a tty the port is unbuffered, otherwise
757 Unbuffered input is good if an application runs an interactive
758 subprocess, since any type-ahead input won't go into Guile's buffer
759 and be unavailable to the subprocess.
761 Note that Guile buffering is completely separate from the tty ``line
762 discipline''. In the usual cooked mode on a tty Guile only sees a
763 line of input once the user presses @key{Return}.
766 @rnindex current-output-port
767 @deffn {Scheme Procedure} current-output-port
768 @deffnx {C Function} scm_current_output_port ()
769 @cindex standard output
770 Return the current output port. This is the default port used
771 by many output procedures.
773 Initially this is the @dfn{standard output} in Unix and C terminology.
774 When the standard output is a tty this port is unbuffered, otherwise
777 Unbuffered output to a tty is good for ensuring progress output or a
778 prompt is seen. But an application which always prints whole lines
779 could change to line buffered, or an application with a lot of output
780 could go fully buffered and perhaps make explicit @code{force-output}
781 calls (@pxref{Writing}) at selected points.
784 @deffn {Scheme Procedure} current-error-port
785 @deffnx {C Function} scm_current_error_port ()
786 @cindex standard error output
787 Return the port to which errors and warnings should be sent.
789 Initially this is the @dfn{standard error} in Unix and C terminology.
790 When the standard error is a tty this port is unbuffered, otherwise
794 @deffn {Scheme Procedure} set-current-input-port port
795 @deffnx {Scheme Procedure} set-current-output-port port
796 @deffnx {Scheme Procedure} set-current-error-port port
797 @deffnx {C Function} scm_set_current_input_port (port)
798 @deffnx {C Function} scm_set_current_output_port (port)
799 @deffnx {C Function} scm_set_current_error_port (port)
800 Change the ports returned by @code{current-input-port},
801 @code{current-output-port} and @code{current-error-port}, respectively,
802 so that they use the supplied @var{port} for input or output.
805 @deftypefn {C Function} void scm_dynwind_current_input_port (SCM port)
806 @deftypefnx {C Function} void scm_dynwind_current_output_port (SCM port)
807 @deftypefnx {C Function} void scm_dynwind_current_error_port (SCM port)
808 These functions must be used inside a pair of calls to
809 @code{scm_dynwind_begin} and @code{scm_dynwind_end} (@pxref{Dynamic
810 Wind}). During the dynwind context, the indicated port is set to
813 More precisely, the current port is swapped with a `backup' value
814 whenever the dynwind context is entered or left. The backup value is
815 initialized with the @var{port} argument.
819 @subsection Types of Port
820 @cindex Types of ports
823 [Types of port; how to make them.]
826 * File Ports:: Ports on an operating system file.
827 * String Ports:: Ports on a Scheme string.
828 * Soft Ports:: Ports on arbitrary Scheme procedures.
829 * Void Ports:: Ports on nothing at all.
834 @subsubsection File Ports
838 The following procedures are used to open file ports.
839 See also @ref{Ports and File Descriptors, open}, for an interface
840 to the Unix @code{open} system call.
842 Most systems have limits on how many files can be open, so it's
843 strongly recommended that file ports be closed explicitly when no
844 longer required (@pxref{Ports}).
846 @deffn {Scheme Procedure} open-file filename mode
847 @deffnx {C Function} scm_open_file (filename, mode)
848 Open the file whose name is @var{filename}, and return a port
849 representing that file. The attributes of the port are
850 determined by the @var{mode} string. The way in which this is
851 interpreted is similar to C stdio. The first character must be
852 one of the following:
856 Open an existing file for input.
858 Open a file for output, creating it if it doesn't already exist
859 or removing its contents if it does.
861 Open a file for output, creating it if it doesn't already
862 exist. All writes to the port will go to the end of the file.
863 The "append mode" can be turned off while the port is in use
864 @pxref{Ports and File Descriptors, fcntl}
867 The following additional characters can be appended:
871 Open the port for both input and output. E.g., @code{r+}: open
872 an existing file for both input and output.
874 Create an "unbuffered" port. In this case input and output
875 operations are passed directly to the underlying port
876 implementation without additional buffering. This is likely to
877 slow down I/O operations. The buffering mode can be changed
878 while a port is in use @pxref{Ports and File Descriptors,
881 Add line-buffering to the port. The port output buffer will be
882 automatically flushed whenever a newline character is written.
884 Use binary mode, ensuring that each byte in the file will be read as one
887 To provide this property, the file will be opened with the 8-bit
888 character encoding "ISO-8859-1", ignoring the default port encoding.
889 @xref{Ports}, for more information on port encodings.
891 Note that while it is possible to read and write binary data as
892 characters or strings, it is usually better to treat bytes as octets,
893 and byte sequences as bytevectors. @xref{R6RS Binary Input}, and
894 @ref{R6RS Binary Output}, for more.
896 This option had another historical meaning, for DOS compatibility: in
897 the default (textual) mode, DOS reads a CR-LF sequence as one LF byte.
898 The @code{b} flag prevents this from happening, adding @code{O_BINARY}
899 to the underlying @code{open} call. Still, the flag is generally useful
900 because of its port encoding ramifications.
903 If a file cannot be opened with the access
904 requested, @code{open-file} throws an exception.
906 When the file is opened, its encoding is set to the current
907 @code{%default-port-encoding}, unless the @code{b} flag was supplied.
908 Sometimes it is desirable to honor Emacs-style coding declarations in
909 files@footnote{Guile 2.0.0 to 2.0.7 would do this by default. This
910 behavior was deemed inappropriate and disabled starting from Guile
911 2.0.8.}. When that is the case, the @code{file-encoding} procedure can
912 be used as follows (@pxref{Character Encoding of Source Files,
913 @code{file-encoding}}):
916 (let* ((port (open-input-file file))
917 (encoding (file-encoding port)))
918 (set-port-encoding! port (or encoding (port-encoding port))))
921 In theory we could create read/write ports which were buffered
922 in one direction only. However this isn't included in the
926 @rnindex open-input-file
927 @deffn {Scheme Procedure} open-input-file filename
928 Open @var{filename} for input. Equivalent to
930 (open-file @var{filename} "r")
934 @rnindex open-output-file
935 @deffn {Scheme Procedure} open-output-file filename
936 Open @var{filename} for output. Equivalent to
938 (open-file @var{filename} "w")
942 @deffn {Scheme Procedure} call-with-input-file filename proc
943 @deffnx {Scheme Procedure} call-with-output-file filename proc
944 @rnindex call-with-input-file
945 @rnindex call-with-output-file
946 Open @var{filename} for input or output, and call @code{(@var{proc}
947 port)} with the resulting port. Return the value returned by
948 @var{proc}. @var{filename} is opened as per @code{open-input-file} or
949 @code{open-output-file} respectively, and an error is signaled if it
952 When @var{proc} returns, the port is closed. If @var{proc} does not
953 return (e.g.@: if it throws an error), then the port might not be
954 closed automatically, though it will be garbage collected in the usual
955 way if not otherwise referenced.
958 @deffn {Scheme Procedure} with-input-from-file filename thunk
959 @deffnx {Scheme Procedure} with-output-to-file filename thunk
960 @deffnx {Scheme Procedure} with-error-to-file filename thunk
961 @rnindex with-input-from-file
962 @rnindex with-output-to-file
963 Open @var{filename} and call @code{(@var{thunk})} with the new port
964 setup as respectively the @code{current-input-port},
965 @code{current-output-port}, or @code{current-error-port}. Return the
966 value returned by @var{thunk}. @var{filename} is opened as per
967 @code{open-input-file} or @code{open-output-file} respectively, and an
968 error is signaled if it cannot be opened.
970 When @var{thunk} returns, the port is closed and the previous setting
971 of the respective current port is restored.
973 The current port setting is managed with @code{dynamic-wind}, so the
974 previous value is restored no matter how @var{thunk} exits (eg.@: an
975 exception), and if @var{thunk} is re-entered (via a captured
976 continuation) then it's set again to the @var{filename} port.
978 The port is closed when @var{thunk} returns normally, but not when
979 exited via an exception or new continuation. This ensures it's still
980 ready for use if @var{thunk} is re-entered by a captured continuation.
981 Of course the port is always garbage collected and closed in the usual
982 way when no longer referenced anywhere.
985 @deffn {Scheme Procedure} port-mode port
986 @deffnx {C Function} scm_port_mode (port)
987 Return the port modes associated with the open port @var{port}.
988 These will not necessarily be identical to the modes used when
989 the port was opened, since modes such as "append" which are
990 used only during port creation are not retained.
993 @deffn {Scheme Procedure} port-filename port
994 @deffnx {C Function} scm_port_filename (port)
995 Return the filename associated with @var{port}, or @code{#f} if no
996 filename is associated with the port.
998 @var{port} must be open, @code{port-filename} cannot be used once the
1002 @deffn {Scheme Procedure} set-port-filename! port filename
1003 @deffnx {C Function} scm_set_port_filename_x (port, filename)
1004 Change the filename associated with @var{port}, using the current input
1005 port if none is specified. Note that this does not change the port's
1006 source of data, but only the value that is returned by
1007 @code{port-filename} and reported in diagnostic output.
1010 @deffn {Scheme Procedure} file-port? obj
1011 @deffnx {C Function} scm_file_port_p (obj)
1012 Determine whether @var{obj} is a port that is related to a file.
1017 @subsubsection String Ports
1019 @cindex Port, string
1021 The following allow string ports to be opened by analogy to R4RS
1022 file port facilities:
1024 With string ports, the port-encoding is treated differently than other
1025 types of ports. When string ports are created, they do not inherit a
1026 character encoding from the current locale. They are given a
1027 default locale that allows them to handle all valid string characters.
1028 Typically one should not modify a string port's character encoding
1029 away from its default.
1031 @deffn {Scheme Procedure} call-with-output-string proc
1032 @deffnx {C Function} scm_call_with_output_string (proc)
1033 Calls the one-argument procedure @var{proc} with a newly created output
1034 port. When the function returns, the string composed of the characters
1035 written into the port is returned. @var{proc} should not close the port.
1037 Note that which characters can be written to a string port depend on the port's
1038 encoding. The default encoding of string ports is specified by the
1039 @code{%default-port-encoding} fluid (@pxref{Ports,
1040 @code{%default-port-encoding}}). For instance, it is an error to write Greek
1041 letter alpha to an ISO-8859-1-encoded string port since this character cannot be
1042 represented with ISO-8859-1:
1045 (define alpha (integer->char #x03b1)) ; GREEK SMALL LETTER ALPHA
1047 (with-fluids ((%default-port-encoding "ISO-8859-1"))
1048 (call-with-output-string
1050 (display alpha p))))
1053 Throw to key `encoding-error'
1056 Changing the string port's encoding to a Unicode-capable encoding such as UTF-8
1060 @deffn {Scheme Procedure} call-with-input-string string proc
1061 @deffnx {C Function} scm_call_with_input_string (string, proc)
1062 Calls the one-argument procedure @var{proc} with a newly
1063 created input port from which @var{string}'s contents may be
1064 read. The value yielded by the @var{proc} is returned.
1067 @deffn {Scheme Procedure} with-output-to-string thunk
1068 Calls the zero-argument procedure @var{thunk} with the current output
1069 port set temporarily to a new string port. It returns a string
1070 composed of the characters written to the current output.
1072 See @code{call-with-output-string} above for character encoding considerations.
1075 @deffn {Scheme Procedure} with-input-from-string string thunk
1076 Calls the zero-argument procedure @var{thunk} with the current input
1077 port set temporarily to a string port opened on the specified
1078 @var{string}. The value yielded by @var{thunk} is returned.
1081 @deffn {Scheme Procedure} open-input-string str
1082 @deffnx {C Function} scm_open_input_string (str)
1083 Take a string and return an input port that delivers characters
1084 from the string. The port can be closed by
1085 @code{close-input-port}, though its storage will be reclaimed
1086 by the garbage collector if it becomes inaccessible.
1089 @deffn {Scheme Procedure} open-output-string
1090 @deffnx {C Function} scm_open_output_string ()
1091 Return an output port that will accumulate characters for
1092 retrieval by @code{get-output-string}. The port can be closed
1093 by the procedure @code{close-output-port}, though its storage
1094 will be reclaimed by the garbage collector if it becomes
1098 @deffn {Scheme Procedure} get-output-string port
1099 @deffnx {C Function} scm_get_output_string (port)
1100 Given an output port created by @code{open-output-string},
1101 return a string consisting of the characters that have been
1102 output to the port so far.
1104 @code{get-output-string} must be used before closing @var{port}, once
1105 closed the string cannot be obtained.
1108 A string port can be used in many procedures which accept a port
1109 but which are not dependent on implementation details of fports.
1110 E.g., seeking and truncating will work on a string port,
1111 but trying to extract the file descriptor number will fail.
1115 @subsubsection Soft Ports
1119 A @dfn{soft-port} is a port based on a vector of procedures capable of
1120 accepting or delivering characters. It allows emulation of I/O ports.
1122 @deffn {Scheme Procedure} make-soft-port pv modes
1123 @deffnx {C Function} scm_make_soft_port (pv, modes)
1124 Return a port capable of receiving or delivering characters as
1125 specified by the @var{modes} string (@pxref{File Ports,
1126 open-file}). @var{pv} must be a vector of length 5 or 6. Its
1127 components are as follows:
1131 procedure accepting one character for output
1133 procedure accepting a string for output
1135 thunk for flushing output
1137 thunk for getting one character
1139 thunk for closing port (not by garbage collection)
1141 (if present and not @code{#f}) thunk for computing the number of
1142 characters that can be read from the port without blocking.
1145 For an output-only port only elements 0, 1, 2, and 4 need be
1146 procedures. For an input-only port only elements 3 and 4 need
1147 be procedures. Thunks 2 and 4 can instead be @code{#f} if
1148 there is no useful operation for them to perform.
1150 If thunk 3 returns @code{#f} or an @code{eof-object}
1151 (@pxref{Input, eof-object?, ,r5rs, The Revised^5 Report on
1152 Scheme}) it indicates that the port has reached end-of-file.
1156 (define stdout (current-output-port))
1157 (define p (make-soft-port
1159 (lambda (c) (write c stdout))
1160 (lambda (s) (display s stdout))
1161 (lambda () (display "." stdout))
1162 (lambda () (char-upcase (read-char)))
1163 (lambda () (display "@@" stdout)))
1166 (write p p) @result{} #<input-output: soft 8081e20>
1172 @subsubsection Void Ports
1176 This kind of port causes any data to be discarded when written to, and
1177 always returns the end-of-file object when read from.
1179 @deffn {Scheme Procedure} %make-void-port mode
1180 @deffnx {C Function} scm_sys_make_void_port (mode)
1181 Create and return a new void port. A void port acts like
1182 @file{/dev/null}. The @var{mode} argument
1183 specifies the input/output modes for this port: see the
1184 documentation for @code{open-file} in @ref{File Ports}.
1188 @node R6RS I/O Ports
1189 @subsection R6RS I/O Ports
1194 The I/O port API of the @uref{http://www.r6rs.org/, Revised Report^6 on
1195 the Algorithmic Language Scheme (R6RS)} is provided by the @code{(rnrs
1196 io ports)} module. It provides features, such as binary I/O and Unicode
1197 string I/O, that complement or refine Guile's historical port API
1198 presented above (@pxref{Input and Output}). Note that R6RS ports are not
1199 disjoint from Guile's native ports, so Guile-specific procedures will
1200 work on ports created using the R6RS API, and vice versa.
1202 The text in this section is taken from the R6RS standard libraries
1203 document, with only minor adaptions for inclusion in this manual. The
1204 Guile developers offer their thanks to the R6RS editors for having
1205 provided the report's text under permissive conditions making this
1208 @c FIXME: Update description when implemented.
1209 @emph{Note}: The implementation of this R6RS API is not complete yet.
1212 * R6RS File Names:: File names.
1213 * R6RS File Options:: Options for opening files.
1214 * R6RS Buffer Modes:: Influencing buffering behavior.
1215 * R6RS Transcoders:: Influencing port encoding.
1216 * R6RS End-of-File:: The end-of-file object.
1217 * R6RS Port Manipulation:: Manipulating R6RS ports.
1218 * R6RS Input Ports:: Input Ports.
1219 * R6RS Binary Input:: Binary input.
1220 * R6RS Textual Input:: Textual input.
1221 * R6RS Output Ports:: Output Ports.
1222 * R6RS Binary Output:: Binary output.
1223 * R6RS Textual Output:: Textual output.
1226 A subset of the @code{(rnrs io ports)} module is provided by the
1227 @code{(ice-9 binary-ports)} module. It contains binary input/output
1228 procedures and does not rely on R6RS support.
1230 @node R6RS File Names
1231 @subsubsection File Names
1233 Some of the procedures described in this chapter accept a file name as an
1234 argument. Valid values for such a file name include strings that name a file
1235 using the native notation of file system paths on an implementation's
1236 underlying operating system, and may include implementation-dependent
1239 A @var{filename} parameter name means that the
1240 corresponding argument must be a file name.
1242 @node R6RS File Options
1243 @subsubsection File Options
1244 @cindex file options
1246 When opening a file, the various procedures in this library accept a
1247 @code{file-options} object that encapsulates flags to specify how the
1248 file is to be opened. A @code{file-options} object is an enum-set
1249 (@pxref{rnrs enums}) over the symbols constituting valid file options.
1251 A @var{file-options} parameter name means that the corresponding
1252 argument must be a file-options object.
1254 @deffn {Scheme Syntax} file-options @var{file-options-symbol} ...
1256 Each @var{file-options-symbol} must be a symbol.
1258 The @code{file-options} syntax returns a file-options object that
1259 encapsulates the specified options.
1261 When supplied to an operation that opens a file for output, the
1262 file-options object returned by @code{(file-options)} specifies that the
1263 file is created if it does not exist and an exception with condition
1264 type @code{&i/o-file-already-exists} is raised if it does exist. The
1265 following standard options can be included to modify the default
1270 If the file does not already exist, it is not created;
1271 instead, an exception with condition type @code{&i/o-file-does-not-exist}
1273 If the file already exists, the exception with condition type
1274 @code{&i/o-file-already-exists} is not raised
1275 and the file is truncated to zero length.
1277 If the file already exists, the exception with condition type
1278 @code{&i/o-file-already-exists} is not raised,
1279 even if @code{no-create} is not included,
1280 and the file is truncated to zero length.
1282 If the file already exists and the exception with condition type
1283 @code{&i/o-file-already-exists} has been inhibited by inclusion of
1284 @code{no-create} or @code{no-fail}, the file is not truncated, but
1285 the port's current position is still set to the beginning of the
1289 These options have no effect when a file is opened only for input.
1290 Symbols other than those listed above may be used as
1291 @var{file-options-symbol}s; they have implementation-specific meaning,
1295 Only the name of @var{file-options-symbol} is significant.
1299 @node R6RS Buffer Modes
1300 @subsubsection Buffer Modes
1302 Each port has an associated buffer mode. For an output port, the
1303 buffer mode defines when an output operation flushes the buffer
1304 associated with the output port. For an input port, the buffer mode
1305 defines how much data will be read to satisfy read operations. The
1306 possible buffer modes are the symbols @code{none} for no buffering,
1307 @code{line} for flushing upon line endings and reading up to line
1308 endings, or other implementation-dependent behavior,
1309 and @code{block} for arbitrary buffering. This section uses
1310 the parameter name @var{buffer-mode} for arguments that must be
1311 buffer-mode symbols.
1313 If two ports are connected to the same mutable source, both ports
1314 are unbuffered, and reading a byte or character from that shared
1315 source via one of the two ports would change the bytes or characters
1316 seen via the other port, a lookahead operation on one port will
1317 render the peeked byte or character inaccessible via the other port,
1318 while a subsequent read operation on the peeked port will see the
1319 peeked byte or character even though the port is otherwise unbuffered.
1321 In other words, the semantics of buffering is defined in terms of side
1322 effects on shared mutable sources, and a lookahead operation has the
1323 same side effect on the shared source as a read operation.
1325 @deffn {Scheme Syntax} buffer-mode @var{buffer-mode-symbol}
1327 @var{buffer-mode-symbol} must be a symbol whose name is one of
1328 @code{none}, @code{line}, and @code{block}. The result is the
1329 corresponding symbol, and specifies the associated buffer mode.
1332 Only the name of @var{buffer-mode-symbol} is significant.
1336 @deffn {Scheme Procedure} buffer-mode? obj
1337 Returns @code{#t} if the argument is a valid buffer-mode symbol, and
1338 returns @code{#f} otherwise.
1341 @node R6RS Transcoders
1342 @subsubsection Transcoders
1344 @cindex end-of-line style
1347 @cindex textual port
1349 Several different Unicode encoding schemes describe standard ways to
1350 encode characters and strings as byte sequences and to decode those
1351 sequences. Within this document, a @dfn{codec} is an immutable Scheme
1352 object that represents a Unicode or similar encoding scheme.
1354 An @dfn{end-of-line style} is a symbol that, if it is not @code{none},
1355 describes how a textual port transcodes representations of line endings.
1357 A @dfn{transcoder} is an immutable Scheme object that combines a codec
1358 with an end-of-line style and a method for handling decoding errors.
1359 Each transcoder represents some specific bidirectional (but not
1360 necessarily lossless), possibly stateful translation between byte
1361 sequences and Unicode characters and strings. Every transcoder can
1362 operate in the input direction (bytes to characters) or in the output
1363 direction (characters to bytes). A @var{transcoder} parameter name
1364 means that the corresponding argument must be a transcoder.
1366 A @dfn{binary port} is a port that supports binary I/O, does not have an
1367 associated transcoder and does not support textual I/O. A @dfn{textual
1368 port} is a port that supports textual I/O, and does not support binary
1369 I/O. A textual port may or may not have an associated transcoder.
1371 @deffn {Scheme Procedure} latin-1-codec
1372 @deffnx {Scheme Procedure} utf-8-codec
1373 @deffnx {Scheme Procedure} utf-16-codec
1375 These are predefined codecs for the ISO 8859-1, UTF-8, and UTF-16
1378 A call to any of these procedures returns a value that is equal in the
1379 sense of @code{eqv?} to the result of any other call to the same
1383 @deffn {Scheme Syntax} eol-style @var{eol-style-symbol}
1385 @var{eol-style-symbol} should be a symbol whose name is one of
1386 @code{lf}, @code{cr}, @code{crlf}, @code{nel}, @code{crnel}, @code{ls},
1389 The form evaluates to the corresponding symbol. If the name of
1390 @var{eol-style-symbol} is not one of these symbols, the effect and
1391 result are implementation-dependent; in particular, the result may be an
1392 eol-style symbol acceptable as an @var{eol-style} argument to
1393 @code{make-transcoder}. Otherwise, an exception is raised.
1395 All eol-style symbols except @code{none} describe a specific
1396 line-ending encoding:
1404 carriage return, linefeed
1408 carriage return, next line
1413 For a textual port with a transcoder, and whose transcoder has an
1414 eol-style symbol @code{none}, no conversion occurs. For a textual input
1415 port, any eol-style symbol other than @code{none} means that all of the
1416 above line-ending encodings are recognized and are translated into a
1417 single linefeed. For a textual output port, @code{none} and @code{lf}
1418 are equivalent. Linefeed characters are encoded according to the
1419 specified eol-style symbol, and all other characters that participate in
1420 possible line endings are encoded as is.
1423 Only the name of @var{eol-style-symbol} is significant.
1427 @deffn {Scheme Procedure} native-eol-style
1428 Returns the default end-of-line style of the underlying platform, e.g.,
1429 @code{lf} on Unix and @code{crlf} on Windows.
1432 @deffn {Condition Type} &i/o-decoding
1433 @deffnx {Scheme Procedure} make-i/o-decoding-error port
1434 @deffnx {Scheme Procedure} i/o-decoding-error? obj
1436 This condition type could be defined by
1439 (define-condition-type &i/o-decoding &i/o-port
1440 make-i/o-decoding-error i/o-decoding-error?)
1443 An exception with this type is raised when one of the operations for
1444 textual input from a port encounters a sequence of bytes that cannot be
1445 translated into a character or string by the input direction of the
1448 When such an exception is raised, the port's position is past the
1452 @deffn {Condition Type} &i/o-encoding
1453 @deffnx {Scheme Procedure} make-i/o-encoding-error port char
1454 @deffnx {Scheme Procedure} i/o-encoding-error? obj
1455 @deffnx {Scheme Procedure} i/o-encoding-error-char condition
1457 This condition type could be defined by
1460 (define-condition-type &i/o-encoding &i/o-port
1461 make-i/o-encoding-error i/o-encoding-error?
1462 (char i/o-encoding-error-char))
1465 An exception with this type is raised when one of the operations for
1466 textual output to a port encounters a character that cannot be
1467 translated into bytes by the output direction of the port's transcoder.
1468 @var{char} is the character that could not be encoded.
1471 @deffn {Scheme Syntax} error-handling-mode @var{error-handling-mode-symbol}
1473 @var{error-handling-mode-symbol} should be a symbol whose name is one of
1474 @code{ignore}, @code{raise}, and @code{replace}. The form evaluates to
1475 the corresponding symbol. If @var{error-handling-mode-symbol} is not
1476 one of these identifiers, effect and result are
1477 implementation-dependent: The result may be an error-handling-mode
1478 symbol acceptable as a @var{handling-mode} argument to
1479 @code{make-transcoder}. If it is not acceptable as a
1480 @var{handling-mode} argument to @code{make-transcoder}, an exception is
1484 Only the name of @var{error-handling-mode-symbol} is significant.
1487 The error-handling mode of a transcoder specifies the behavior
1488 of textual I/O operations in the presence of encoding or decoding
1491 If a textual input operation encounters an invalid or incomplete
1492 character encoding, and the error-handling mode is @code{ignore}, an
1493 appropriate number of bytes of the invalid encoding are ignored and
1494 decoding continues with the following bytes.
1496 If the error-handling mode is @code{replace}, the replacement
1497 character U+FFFD is injected into the data stream, an appropriate
1498 number of bytes are ignored, and decoding
1499 continues with the following bytes.
1501 If the error-handling mode is @code{raise}, an exception with condition
1502 type @code{&i/o-decoding} is raised.
1504 If a textual output operation encounters a character it cannot encode,
1505 and the error-handling mode is @code{ignore}, the character is ignored
1506 and encoding continues with the next character. If the error-handling
1507 mode is @code{replace}, a codec-specific replacement character is
1508 emitted by the transcoder, and encoding continues with the next
1509 character. The replacement character is U+FFFD for transcoders whose
1510 codec is one of the Unicode encodings, but is the @code{?} character
1511 for the Latin-1 encoding. If the error-handling mode is @code{raise},
1512 an exception with condition type @code{&i/o-encoding} is raised.
1515 @deffn {Scheme Procedure} make-transcoder codec
1516 @deffnx {Scheme Procedure} make-transcoder codec eol-style
1517 @deffnx {Scheme Procedure} make-transcoder codec eol-style handling-mode
1519 @var{codec} must be a codec; @var{eol-style}, if present, an eol-style
1520 symbol; and @var{handling-mode}, if present, an error-handling-mode
1523 @var{eol-style} may be omitted, in which case it defaults to the native
1524 end-of-line style of the underlying platform. @var{handling-mode} may
1525 be omitted, in which case it defaults to @code{replace}. The result is
1526 a transcoder with the behavior specified by its arguments.
1529 @deffn {Scheme procedure} native-transcoder
1530 Returns an implementation-dependent transcoder that represents a
1531 possibly locale-dependent ``native'' transcoding.
1534 @deffn {Scheme Procedure} transcoder-codec transcoder
1535 @deffnx {Scheme Procedure} transcoder-eol-style transcoder
1536 @deffnx {Scheme Procedure} transcoder-error-handling-mode transcoder
1538 These are accessors for transcoder objects; when applied to a
1539 transcoder returned by @code{make-transcoder}, they return the
1540 @var{codec}, @var{eol-style}, and @var{handling-mode} arguments,
1544 @deffn {Scheme Procedure} bytevector->string bytevector transcoder
1546 Returns the string that results from transcoding the
1547 @var{bytevector} according to the input direction of the transcoder.
1550 @deffn {Scheme Procedure} string->bytevector string transcoder
1552 Returns the bytevector that results from transcoding the
1553 @var{string} according to the output direction of the transcoder.
1556 @node R6RS End-of-File
1557 @subsubsection The End-of-File Object
1562 R5RS' @code{eof-object?} procedure is provided by the @code{(rnrs io
1565 @deffn {Scheme Procedure} eof-object? obj
1566 @deffnx {C Function} scm_eof_object_p (obj)
1567 Return true if @var{obj} is the end-of-file (EOF) object.
1570 In addition, the following procedure is provided:
1572 @deffn {Scheme Procedure} eof-object
1573 @deffnx {C Function} scm_eof_object ()
1574 Return the end-of-file (EOF) object.
1577 (eof-object? (eof-object))
1583 @node R6RS Port Manipulation
1584 @subsubsection Port Manipulation
1586 The procedures listed below operate on any kind of R6RS I/O port.
1588 @deffn {Scheme Procedure} port? obj
1589 Returns @code{#t} if the argument is a port, and returns @code{#f}
1593 @deffn {Scheme Procedure} port-transcoder port
1594 Returns the transcoder associated with @var{port} if @var{port} is
1595 textual and has an associated transcoder, and returns @code{#f} if
1596 @var{port} is binary or does not have an associated transcoder.
1599 @deffn {Scheme Procedure} binary-port? port
1600 Return @code{#t} if @var{port} is a @dfn{binary port}, suitable for
1601 binary data input/output.
1603 Note that internally Guile does not differentiate between binary and
1604 textual ports, unlike the R6RS. Thus, this procedure returns true when
1605 @var{port} does not have an associated encoding---i.e., when
1606 @code{(port-encoding @var{port})} is @code{#f} (@pxref{Ports,
1607 port-encoding}). This is the case for ports returned by R6RS procedures
1608 such as @code{open-bytevector-input-port} and
1609 @code{make-custom-binary-output-port}.
1611 However, Guile currently does not prevent use of textual I/O procedures
1612 such as @code{display} or @code{read-char} with binary ports. Doing so
1613 ``upgrades'' the port from binary to textual, under the ISO-8859-1
1614 encoding. Likewise, Guile does not prevent use of
1615 @code{set-port-encoding!} on a binary port, which also turns it into a
1619 @deffn {Scheme Procedure} textual-port? port
1620 Always return @code{#t}, as all ports can be used for textual I/O in
1624 @deffn {Scheme Procedure} transcoded-port binary-port transcoder
1625 The @code{transcoded-port} procedure
1626 returns a new textual port with the specified @var{transcoder}.
1627 Otherwise the new textual port's state is largely the same as
1628 that of @var{binary-port}.
1629 If @var{binary-port} is an input port, the new textual
1630 port will be an input port and
1631 will transcode the bytes that have not yet been read from
1633 If @var{binary-port} is an output port, the new textual
1634 port will be an output port and
1635 will transcode output characters into bytes that are
1636 written to the byte sink represented by @var{binary-port}.
1638 As a side effect, however, @code{transcoded-port}
1639 closes @var{binary-port} in
1640 a special way that allows the new textual port to continue to
1641 use the byte source or sink represented by @var{binary-port},
1642 even though @var{binary-port} itself is closed and cannot
1643 be used by the input and output operations described in this
1647 @deffn {Scheme Procedure} port-position port
1648 If @var{port} supports it (see below), return the offset (an integer)
1649 indicating where the next octet will be read from/written to in
1650 @var{port}. If @var{port} does not support this operation, an error
1651 condition is raised.
1653 This is similar to Guile's @code{seek} procedure with the
1654 @code{SEEK_CUR} argument (@pxref{Random Access}).
1657 @deffn {Scheme Procedure} port-has-port-position? port
1658 Return @code{#t} is @var{port} supports @code{port-position}.
1661 @deffn {Scheme Procedure} set-port-position! port offset
1662 If @var{port} supports it (see below), set the position where the next
1663 octet will be read from/written to @var{port} to @var{offset} (an
1664 integer). If @var{port} does not support this operation, an error
1665 condition is raised.
1667 This is similar to Guile's @code{seek} procedure with the
1668 @code{SEEK_SET} argument (@pxref{Random Access}).
1671 @deffn {Scheme Procedure} port-has-set-port-position!? port
1672 Return @code{#t} is @var{port} supports @code{set-port-position!}.
1675 @deffn {Scheme Procedure} call-with-port port proc
1676 Call @var{proc}, passing it @var{port} and closing @var{port} upon exit
1677 of @var{proc}. Return the return values of @var{proc}.
1680 @node R6RS Input Ports
1681 @subsubsection Input Ports
1683 @deffn {Scheme Procedure} input-port? obj
1684 Returns @code{#t} if the argument is an input port (or a combined input
1685 and output port), and returns @code{#f} otherwise.
1688 @deffn {Scheme Procedure} port-eof? input-port
1690 if the @code{lookahead-u8} procedure (if @var{input-port} is a binary port)
1691 or the @code{lookahead-char} procedure (if @var{input-port} is a textual port)
1693 the end-of-file object, and @code{#f} otherwise.
1694 The operation may block indefinitely if no data is available
1695 but the port cannot be determined to be at end of file.
1698 @deffn {Scheme Procedure} open-file-input-port filename
1699 @deffnx {Scheme Procedure} open-file-input-port filename file-options
1700 @deffnx {Scheme Procedure} open-file-input-port filename file-options buffer-mode
1701 @deffnx {Scheme Procedure} open-file-input-port filename file-options buffer-mode maybe-transcoder
1702 @var{maybe-transcoder} must be either a transcoder or @code{#f}.
1704 The @code{open-file-input-port} procedure returns an
1705 input port for the named file. The @var{file-options} and
1706 @var{maybe-transcoder} arguments are optional.
1708 The @var{file-options} argument, which may determine
1709 various aspects of the returned port (@pxref{R6RS File Options}),
1710 defaults to the value of @code{(file-options)}.
1712 The @var{buffer-mode} argument, if supplied,
1713 must be one of the symbols that name a buffer mode.
1714 The @var{buffer-mode} argument defaults to @code{block}.
1716 If @var{maybe-transcoder} is a transcoder, it becomes the transcoder associated
1717 with the returned port.
1719 If @var{maybe-transcoder} is @code{#f} or absent,
1720 the port will be a binary port and will support the
1721 @code{port-position} and @code{set-port-position!} operations.
1722 Otherwise the port will be a textual port, and whether it supports
1723 the @code{port-position} and @code{set-port-position!} operations
1724 is implementation-dependent (and possibly transcoder-dependent).
1727 @deffn {Scheme Procedure} standard-input-port
1728 Returns a fresh binary input port connected to standard input. Whether
1729 the port supports the @code{port-position} and @code{set-port-position!}
1730 operations is implementation-dependent.
1733 @deffn {Scheme Procedure} current-input-port
1734 This returns a default textual port for input. Normally, this default
1735 port is associated with standard input, but can be dynamically
1736 re-assigned using the @code{with-input-from-file} procedure from the
1737 @code{io simple (6)} library (@pxref{rnrs io simple}). The port may or
1738 may not have an associated transcoder; if it does, the transcoder is
1739 implementation-dependent.
1742 @node R6RS Binary Input
1743 @subsubsection Binary Input
1745 @cindex binary input
1747 R6RS binary input ports can be created with the procedures described
1750 @deffn {Scheme Procedure} open-bytevector-input-port bv [transcoder]
1751 @deffnx {C Function} scm_open_bytevector_input_port (bv, transcoder)
1752 Return an input port whose contents are drawn from bytevector @var{bv}
1753 (@pxref{Bytevectors}).
1755 @c FIXME: Update description when implemented.
1756 The @var{transcoder} argument is currently not supported.
1759 @cindex custom binary input ports
1761 @deffn {Scheme Procedure} make-custom-binary-input-port id read! get-position set-position! close
1762 @deffnx {C Function} scm_make_custom_binary_input_port (id, read!, get-position, set-position!, close)
1763 Return a new custom binary input port@footnote{This is similar in spirit
1764 to Guile's @dfn{soft ports} (@pxref{Soft Ports}).} named @var{id} (a
1765 string) whose input is drained by invoking @var{read!} and passing it a
1766 bytevector, an index where bytes should be written, and the number of
1767 bytes to read. The @code{read!} procedure must return an integer
1768 indicating the number of bytes read, or @code{0} to indicate the
1771 Optionally, if @var{get-position} is not @code{#f}, it must be a thunk
1772 that will be called when @code{port-position} is invoked on the custom
1773 binary port and should return an integer indicating the position within
1774 the underlying data stream; if @var{get-position} was not supplied, the
1775 returned port does not support @code{port-position}.
1777 Likewise, if @var{set-position!} is not @code{#f}, it should be a
1778 one-argument procedure. When @code{set-port-position!} is invoked on the
1779 custom binary input port, @var{set-position!} is passed an integer
1780 indicating the position of the next byte is to read.
1782 Finally, if @var{close} is not @code{#f}, it must be a thunk. It is
1783 invoked when the custom binary input port is closed.
1785 Using a custom binary input port, the @code{open-bytevector-input-port}
1786 procedure could be implemented as follows:
1789 (define (open-bytevector-input-port source)
1791 (define length (bytevector-length source))
1793 (define (read! bv start count)
1794 (let ((count (min count (- length position))))
1795 (bytevector-copy! source position
1797 (set! position (+ position count))
1800 (define (get-position) position)
1802 (define (set-position! new-position)
1803 (set! position new-position))
1805 (make-custom-binary-input-port "the port" read!
1809 (read (open-bytevector-input-port (string->utf8 "hello")))
1814 @cindex binary input
1815 Binary input is achieved using the procedures below:
1817 @deffn {Scheme Procedure} get-u8 port
1818 @deffnx {C Function} scm_get_u8 (port)
1819 Return an octet read from @var{port}, a binary input port, blocking as
1820 necessary, or the end-of-file object.
1823 @deffn {Scheme Procedure} lookahead-u8 port
1824 @deffnx {C Function} scm_lookahead_u8 (port)
1825 Like @code{get-u8} but does not update @var{port}'s position to point
1829 @deffn {Scheme Procedure} get-bytevector-n port count
1830 @deffnx {C Function} scm_get_bytevector_n (port, count)
1831 Read @var{count} octets from @var{port}, blocking as necessary and
1832 return a bytevector containing the octets read. If fewer bytes are
1833 available, a bytevector smaller than @var{count} is returned.
1836 @deffn {Scheme Procedure} get-bytevector-n! port bv start count
1837 @deffnx {C Function} scm_get_bytevector_n_x (port, bv, start, count)
1838 Read @var{count} bytes from @var{port} and store them in @var{bv}
1839 starting at index @var{start}. Return either the number of bytes
1840 actually read or the end-of-file object.
1843 @deffn {Scheme Procedure} get-bytevector-some port
1844 @deffnx {C Function} scm_get_bytevector_some (port)
1845 Read from @var{port}, blocking as necessary, until bytes are available
1846 or an end-of-file is reached. Return either the end-of-file object or a
1847 new bytevector containing some of the available bytes (at least one),
1848 and update the port position to point just past these bytes.
1851 @deffn {Scheme Procedure} get-bytevector-all port
1852 @deffnx {C Function} scm_get_bytevector_all (port)
1853 Read from @var{port}, blocking as necessary, until the end-of-file is
1854 reached. Return either a new bytevector containing the data read or the
1855 end-of-file object (if no data were available).
1858 @node R6RS Textual Input
1859 @subsubsection Textual Input
1861 @deffn {Scheme Procedure} get-char textual-input-port
1862 Reads from @var{textual-input-port}, blocking as necessary, until a
1863 complete character is available from @var{textual-input-port},
1864 or until an end of file is reached.
1866 If a complete character is available before the next end of file,
1867 @code{get-char} returns that character and updates the input port to
1868 point past the character. If an end of file is reached before any
1869 character is read, @code{get-char} returns the end-of-file object.
1872 @deffn {Scheme Procedure} lookahead-char textual-input-port
1873 The @code{lookahead-char} procedure is like @code{get-char}, but it does
1874 not update @var{textual-input-port} to point past the character.
1877 @deffn {Scheme Procedure} get-string-n textual-input-port count
1879 @var{count} must be an exact, non-negative integer object, representing
1880 the number of characters to be read.
1882 The @code{get-string-n} procedure reads from @var{textual-input-port},
1883 blocking as necessary, until @var{count} characters are available, or
1884 until an end of file is reached.
1886 If @var{count} characters are available before end of file,
1887 @code{get-string-n} returns a string consisting of those @var{count}
1888 characters. If fewer characters are available before an end of file, but
1889 one or more characters can be read, @code{get-string-n} returns a string
1890 containing those characters. In either case, the input port is updated
1891 to point just past the characters read. If no characters can be read
1892 before an end of file, the end-of-file object is returned.
1895 @deffn {Scheme Procedure} get-string-n! textual-input-port string start count
1897 @var{start} and @var{count} must be exact, non-negative integer objects,
1898 with @var{count} representing the number of characters to be read.
1899 @var{string} must be a string with at least $@var{start} + @var{count}$
1902 The @code{get-string-n!} procedure reads from @var{textual-input-port}
1903 in the same manner as @code{get-string-n}. If @var{count} characters
1904 are available before an end of file, they are written into @var{string}
1905 starting at index @var{start}, and @var{count} is returned. If fewer
1906 characters are available before an end of file, but one or more can be
1907 read, those characters are written into @var{string} starting at index
1908 @var{start} and the number of characters actually read is returned as an
1909 exact integer object. If no characters can be read before an end of
1910 file, the end-of-file object is returned.
1913 @deffn {Scheme Procedure} get-string-all textual-input-port count
1914 Reads from @var{textual-input-port} until an end of file, decoding
1915 characters in the same manner as @code{get-string-n} and
1916 @code{get-string-n!}.
1918 If characters are available before the end of file, a string containing
1919 all the characters decoded from that data are returned. If no character
1920 precedes the end of file, the end-of-file object is returned.
1923 @deffn {Scheme Procedure} get-line textual-input-port
1924 Reads from @var{textual-input-port} up to and including the linefeed
1925 character or end of file, decoding characters in the same manner as
1926 @code{get-string-n} and @code{get-string-n!}.
1928 If a linefeed character is read, a string containing all of the text up
1929 to (but not including) the linefeed character is returned, and the port
1930 is updated to point just past the linefeed character. If an end of file
1931 is encountered before any linefeed character is read, but some
1932 characters have been read and decoded as characters, a string containing
1933 those characters is returned. If an end of file is encountered before
1934 any characters are read, the end-of-file object is returned.
1937 The end-of-line style, if not @code{none}, will cause all line endings
1938 to be read as linefeed characters. @xref{R6RS Transcoders}.
1942 @deffn {Scheme Procedure} get-datum textual-input-port count
1943 Reads an external representation from @var{textual-input-port} and returns the
1944 datum it represents. The @code{get-datum} procedure returns the next
1945 datum that can be parsed from the given @var{textual-input-port}, updating
1946 @var{textual-input-port} to point exactly past the end of the external
1947 representation of the object.
1949 Any @emph{interlexeme space} (comment or whitespace, @pxref{Scheme
1950 Syntax}) in the input is first skipped. If an end of file occurs after
1951 the interlexeme space, the end-of-file object (@pxref{R6RS End-of-File})
1954 If a character inconsistent with an external representation is
1955 encountered in the input, an exception with condition types
1956 @code{&lexical} and @code{&i/o-read} is raised. Also, if the end of
1957 file is encountered after the beginning of an external representation,
1958 but the external representation is incomplete and therefore cannot be
1959 parsed, an exception with condition types @code{&lexical} and
1960 @code{&i/o-read} is raised.
1963 @node R6RS Output Ports
1964 @subsubsection Output Ports
1966 @deffn {Scheme Procedure} output-port? obj
1967 Returns @code{#t} if the argument is an output port (or a
1968 combined input and output port), @code{#f} otherwise.
1971 @deffn {Scheme Procedure} flush-output-port port
1972 Flushes any buffered output from the buffer of @var{output-port} to the
1973 underlying file, device, or object. The @code{flush-output-port}
1974 procedure returns an unspecified values.
1977 @deffn {Scheme Procedure} open-file-output-port filename
1978 @deffnx {Scheme Procedure} open-file-output-port filename file-options
1979 @deffnx {Scheme Procedure} open-file-output-port filename file-options buffer-mode
1980 @deffnx {Scheme Procedure} open-file-output-port filename file-options buffer-mode maybe-transcoder
1982 @var{maybe-transcoder} must be either a transcoder or @code{#f}.
1984 The @code{open-file-output-port} procedure returns an output port for the named file.
1986 The @var{file-options} argument, which may determine various aspects of
1987 the returned port (@pxref{R6RS File Options}), defaults to the value of
1988 @code{(file-options)}.
1990 The @var{buffer-mode} argument, if supplied,
1991 must be one of the symbols that name a buffer mode.
1992 The @var{buffer-mode} argument defaults to @code{block}.
1994 If @var{maybe-transcoder} is a transcoder, it becomes the transcoder
1995 associated with the port.
1997 If @var{maybe-transcoder} is @code{#f} or absent,
1998 the port will be a binary port and will support the
1999 @code{port-position} and @code{set-port-position!} operations.
2000 Otherwise the port will be a textual port, and whether it supports
2001 the @code{port-position} and @code{set-port-position!} operations
2002 is implementation-dependent (and possibly transcoder-dependent).
2005 @deffn {Scheme Procedure} standard-output-port
2006 @deffnx {Scheme Procedure} standard-error-port
2007 Returns a fresh binary output port connected to the standard output or
2008 standard error respectively. Whether the port supports the
2009 @code{port-position} and @code{set-port-position!} operations is
2010 implementation-dependent.
2013 @deffn {Scheme Procedure} current-output-port
2014 @deffnx {Scheme Procedure} current-error-port
2015 These return default textual ports for regular output and error output.
2016 Normally, these default ports are associated with standard output, and
2017 standard error, respectively. The return value of
2018 @code{current-output-port} can be dynamically re-assigned using the
2019 @code{with-output-to-file} procedure from the @code{io simple (6)}
2020 library (@pxref{rnrs io simple}). A port returned by one of these
2021 procedures may or may not have an associated transcoder; if it does, the
2022 transcoder is implementation-dependent.
2025 @node R6RS Binary Output
2026 @subsubsection Binary Output
2028 Binary output ports can be created with the procedures below.
2030 @deffn {Scheme Procedure} open-bytevector-output-port [transcoder]
2031 @deffnx {C Function} scm_open_bytevector_output_port (transcoder)
2032 Return two values: a binary output port and a procedure. The latter
2033 should be called with zero arguments to obtain a bytevector containing
2034 the data accumulated by the port, as illustrated below.
2039 (open-bytevector-output-port))
2040 (lambda (port get-bytevector)
2041 (display "hello" port)
2044 @result{} #vu8(104 101 108 108 111)
2047 @c FIXME: Update description when implemented.
2048 The @var{transcoder} argument is currently not supported.
2051 @cindex custom binary output ports
2053 @deffn {Scheme Procedure} make-custom-binary-output-port id write! get-position set-position! close
2054 @deffnx {C Function} scm_make_custom_binary_output_port (id, write!, get-position, set-position!, close)
2055 Return a new custom binary output port named @var{id} (a string) whose
2056 output is sunk by invoking @var{write!} and passing it a bytevector, an
2057 index where bytes should be read from this bytevector, and the number of
2058 bytes to be ``written''. The @code{write!} procedure must return an
2059 integer indicating the number of bytes actually written; when it is
2060 passed @code{0} as the number of bytes to write, it should behave as
2061 though an end-of-file was sent to the byte sink.
2063 The other arguments are as for @code{make-custom-binary-input-port}
2064 (@pxref{R6RS Binary Input, @code{make-custom-binary-input-port}}).
2067 @cindex binary output
2068 Writing to a binary output port can be done using the following
2071 @deffn {Scheme Procedure} put-u8 port octet
2072 @deffnx {C Function} scm_put_u8 (port, octet)
2073 Write @var{octet}, an integer in the 0--255 range, to @var{port}, a
2077 @deffn {Scheme Procedure} put-bytevector port bv [start [count]]
2078 @deffnx {C Function} scm_put_bytevector (port, bv, start, count)
2079 Write the contents of @var{bv} to @var{port}, optionally starting at
2080 index @var{start} and limiting to @var{count} octets.
2083 @node R6RS Textual Output
2084 @subsubsection Textual Output
2086 @deffn {Scheme Procedure} put-char port char
2087 Writes @var{char} to the port. The @code{put-char} procedure returns
2090 @deffn {Scheme Procedure} put-string port string
2091 @deffnx {Scheme Procedure} put-string port string start
2092 @deffnx {Scheme Procedure} put-string port string start count
2094 @var{start} and @var{count} must be non-negative exact integer objects.
2095 @var{string} must have a length of at least @math{@var{start} +
2096 @var{count}}. @var{start} defaults to 0. @var{count} defaults to
2097 @math{@code{(string-length @var{string})} - @var{start}}$. The
2098 @code{put-string} procedure writes the @var{count} characters of
2099 @var{string} starting at index @var{start} to the port. The
2100 @code{put-string} procedure returns an unspecified value.
2103 @deffn {Scheme Procedure} put-datum textual-output-port datum
2104 @var{datum} should be a datum value. The @code{put-datum} procedure
2105 writes an external representation of @var{datum} to
2106 @var{textual-output-port}. The specific external representation is
2107 implementation-dependent. However, whenever possible, an implementation
2108 should produce a representation for which @code{get-datum}, when reading
2109 the representation, will return an object equal (in the sense of
2110 @code{equal?}) to @var{datum}.
2113 Not all datums may allow producing an external representation for which
2114 @code{get-datum} will produce an object that is equal to the
2115 original. Specifically, NaNs contained in @var{datum} may make
2120 The @code{put-datum} procedure merely writes the external
2121 representation, but no trailing delimiter. If @code{put-datum} is
2122 used to write several subsequent external representations to an
2123 output port, care should be taken to delimit them properly so they can
2124 be read back in by subsequent calls to @code{get-datum}.
2128 @node I/O Extensions
2129 @subsection Using and Extending Ports in C
2132 * C Port Interface:: Using ports from C.
2133 * Port Implementation:: How to implement a new port type in C.
2137 @node C Port Interface
2138 @subsubsection C Port Interface
2139 @cindex C port interface
2140 @cindex Port, C interface
2142 This section describes how to use Scheme ports from C.
2144 @subsubheading Port basics
2147 @tindex scm_ptob_descriptor
2149 @findex SCM_PTAB_ENTRY
2152 There are two main data structures. A port type object (ptob) is of
2153 type @code{scm_ptob_descriptor}. A port instance is of type
2154 @code{scm_port}. Given an @code{SCM} variable which points to a port,
2155 the corresponding C port object can be obtained using the
2156 @code{SCM_PTAB_ENTRY} macro. The ptob can be obtained by using
2157 @code{SCM_PTOBNUM} to give an index into the @code{scm_ptobs}
2160 @subsubheading Port buffers
2162 An input port always has a read buffer and an output port always has a
2163 write buffer. However the size of these buffers is not guaranteed to be
2164 more than one byte (e.g., the @code{shortbuf} field in @code{scm_port}
2165 which is used when no other buffer is allocated). The way in which the
2166 buffers are allocated depends on the implementation of the ptob. For
2167 example in the case of an fport, buffers may be allocated with malloc
2168 when the port is created, but in the case of an strport the underlying
2169 string is used as the buffer.
2171 @subsubheading The @code{rw_random} flag
2173 Special treatment is required for ports which can be seeked at random.
2174 Before various operations, such as seeking the port or changing from
2175 input to output on a bidirectional port or vice versa, the port
2176 implementation must be given a chance to update its state. The write
2177 buffer is updated by calling the @code{flush} ptob procedure and the
2178 input buffer is updated by calling the @code{end_input} ptob procedure.
2179 In the case of an fport, @code{flush} causes buffered output to be
2180 written to the file descriptor, while @code{end_input} causes the
2181 descriptor position to be adjusted to account for buffered input which
2184 The special treatment must be performed if the @code{rw_random} flag in
2185 the port is non-zero.
2187 @subsubheading The @code{rw_active} variable
2189 The @code{rw_active} variable in the port is only used if
2190 @code{rw_random} is set. It's defined as an enum with the following
2195 the read buffer may have unread data.
2197 @item SCM_PORT_WRITE
2198 the write buffer may have unwritten data.
2200 @item SCM_PORT_NEITHER
2201 neither the write nor the read buffer has data.
2204 @subsubheading Reading from a port.
2206 To read from a port, it's possible to either call existing libguile
2207 procedures such as @code{scm_getc} and @code{scm_read_line} or to read
2208 data from the read buffer directly. Reading from the buffer involves
2209 the following steps:
2213 Flush output on the port, if @code{rw_active} is @code{SCM_PORT_WRITE}.
2216 Fill the read buffer, if it's empty, using @code{scm_fill_input}.
2218 @item Read the data from the buffer and update the read position in
2219 the buffer. Steps 2) and 3) may be repeated as many times as required.
2221 @item Set rw_active to @code{SCM_PORT_READ} if @code{rw_random} is set.
2223 @item update the port's line and column counts.
2226 @subsubheading Writing to a port.
2228 To write data to a port, calling @code{scm_lfwrite} should be sufficient for
2229 most purposes. This takes care of the following steps:
2233 End input on the port, if @code{rw_active} is @code{SCM_PORT_READ}.
2236 Pass the data to the ptob implementation using the @code{write} ptob
2237 procedure. The advantage of using the ptob @code{write} instead of
2238 manipulating the write buffer directly is that it allows the data to be
2239 written in one operation even if the port is using the single-byte
2243 Set @code{rw_active} to @code{SCM_PORT_WRITE} if @code{rw_random}
2248 @node Port Implementation
2249 @subsubsection Port Implementation
2250 @cindex Port implementation
2252 This section describes how to implement a new port type in C.
2254 As described in the previous section, a port type object (ptob) is
2255 a structure of type @code{scm_ptob_descriptor}. A ptob is created by
2256 calling @code{scm_make_port_type}.
2258 @deftypefun scm_t_bits scm_make_port_type (char *name, int (*fill_input) (SCM port), void (*write) (SCM port, const void *data, size_t size))
2259 Return a new port type object. The @var{name}, @var{fill_input} and
2260 @var{write} parameters are initial values for those port type fields,
2261 as described below. The other fields are initialized with default
2262 values and can be changed later.
2265 All of the elements of the ptob, apart from @code{name}, are procedures
2266 which collectively implement the port behaviour. Creating a new port
2267 type mostly involves writing these procedures.
2271 A pointer to a NUL terminated string: the name of the port type. This
2272 is the only element of @code{scm_ptob_descriptor} which is not
2273 a procedure. Set via the first argument to @code{scm_make_port_type}.
2276 Called during garbage collection to mark any SCM objects that a port
2277 object may contain. It doesn't need to be set unless the port has
2278 @code{SCM} components. Set using
2280 @deftypefun void scm_set_port_mark (scm_t_bits tc, SCM (*mark) (SCM port))
2284 Called when the port is collected during gc. It
2285 should free any resources used by the port.
2288 @deftypefun void scm_set_port_free (scm_t_bits tc, size_t (*free) (SCM port))
2292 Called when @code{write} is called on the port object, to print a
2293 port description. E.g., for an fport it may produce something like:
2294 @code{#<input: /etc/passwd 3>}. Set using
2296 @deftypefun void scm_set_port_print (scm_t_bits tc, int (*print) (SCM port, SCM dest_port, scm_print_state *pstate))
2297 The first argument @var{port} is the object being printed, the second
2298 argument @var{dest_port} is where its description should go.
2302 Not used at present. Set using
2304 @deftypefun void scm_set_port_equalp (scm_t_bits tc, SCM (*equalp) (SCM, SCM))
2308 Called when the port is closed, unless it was collected during gc. It
2309 should free any resources used by the port.
2312 @deftypefun void scm_set_port_close (scm_t_bits tc, int (*close) (SCM port))
2316 Accept data which is to be written using the port. The port implementation
2317 may choose to buffer the data instead of processing it directly.
2318 Set via the third argument to @code{scm_make_port_type}.
2321 Complete the processing of buffered output data. Reset the value of
2322 @code{rw_active} to @code{SCM_PORT_NEITHER}.
2325 @deftypefun void scm_set_port_flush (scm_t_bits tc, void (*flush) (SCM port))
2329 Perform any synchronization required when switching from input to output
2330 on the port. Reset the value of @code{rw_active} to @code{SCM_PORT_NEITHER}.
2333 @deftypefun void scm_set_port_end_input (scm_t_bits tc, void (*end_input) (SCM port, int offset))
2337 Read new data into the read buffer and return the first character. It
2338 can be assumed that the read buffer is empty when this procedure is called.
2339 Set via the second argument to @code{scm_make_port_type}.
2342 Return a lower bound on the number of bytes that could be read from the
2343 port without blocking. It can be assumed that the current state of
2344 @code{rw_active} is @code{SCM_PORT_NEITHER}.
2347 @deftypefun void scm_set_port_input_waiting (scm_t_bits tc, int (*input_waiting) (SCM port))
2351 Set the current position of the port. The procedure can not make
2352 any assumptions about the value of @code{rw_active} when it's
2353 called. It can reset the buffers first if desired by using something
2357 if (pt->rw_active == SCM_PORT_READ)
2358 scm_end_input (port);
2359 else if (pt->rw_active == SCM_PORT_WRITE)
2363 However note that this will have the side effect of discarding any data
2364 in the unread-char buffer, in addition to any side effects from the
2365 @code{end_input} and @code{flush} ptob procedures. This is undesirable
2366 when seek is called to measure the current position of the port, i.e.,
2367 @code{(seek p 0 SEEK_CUR)}. The libguile fport and string port
2368 implementations take care to avoid this problem.
2370 The procedure is set using
2372 @deftypefun void scm_set_port_seek (scm_t_bits tc, scm_t_off (*seek) (SCM port, scm_t_off offset, int whence))
2376 Truncate the port data to be specified length. It can be assumed that the
2377 current state of @code{rw_active} is @code{SCM_PORT_NEITHER}.
2380 @deftypefun void scm_set_port_truncate (scm_t_bits tc, void (*truncate) (SCM port, scm_t_off length))
2386 @subsection Handling of Unicode byte order marks.
2388 @cindex byte order mark
2390 This section documents the finer points of Guile's handling of Unicode
2391 byte order marks (BOMs). A byte order mark (U+FEFF) is typically found
2392 at the start of a UTF-16 or UTF-32 stream, to allow readers to reliably
2393 determine the byte order. Occasionally, a BOM is found at the start of
2394 a UTF-8 stream, but this is much less common and not generally
2397 Guile attempts to handle BOMs automatically, and in accordance with the
2398 recommendations of the Unicode Standard, when the port encoding is set
2399 to @code{UTF-8}, @code{UTF-16}, or @code{UTF-32}. In brief, Guile
2400 automatically writes a BOM at the start of a UTF-16 or UTF-32 stream,
2401 and automatically consumes one from the start of a UTF-8, UTF-16, or
2404 As specified in the Unicode Standard, a BOM is only handled specially at
2405 the start of a stream, and only if the port encoding is set to
2406 @code{UTF-8}, @code{UTF-16} or @code{UTF-32}. If the port encoding is
2407 set to @code{UTF-16BE}, @code{UTF-16LE}, @code{UTF-32BE}, or
2408 @code{UTF-32LE}, then BOMs are @emph{not} handled specially, and none of
2409 the special handling described in this section applies.
2413 To ensure that Guile will properly detect the byte order of a UTF-16 or
2414 UTF-32 stream, you must perform a textual read before any writes, seeks,
2415 or binary I/O. Guile will not attempt to read a BOM unless a read is
2416 explicitly requested at the start of the stream.
2419 If a textual write is performed before the first read, then an arbitrary
2420 byte order will be chosen. Currently, big endian is the default on all
2421 platforms, but that may change in the future. If you wish to explicitly
2422 control the byte order of an output stream, set the port encoding to
2423 @code{UTF-16BE}, @code{UTF-16LE}, @code{UTF-32BE}, or @code{UTF-32LE},
2424 and explicitly write a BOM (@code{#\xFEFF}) if desired.
2427 If @code{set-port-encoding!} is called in the middle of a stream, Guile
2428 treats this as a new logical ``start of stream'' for purposes of BOM
2429 handling, and will forget about any BOMs that had previously been seen.
2430 Therefore, it may choose a different byte order than had been used
2431 previously. This is intended to support multiple logical text streams
2432 embedded within a larger binary stream.
2435 Binary I/O operations are not guaranteed to update Guile's notion of
2436 whether the port is at the ``start of the stream'', nor are they
2437 guaranteed to produce or consume BOMs.
2440 For ports that support seeking (e.g. normal files), the input and output
2441 streams are considered linked: if the user reads first, then a BOM will
2442 be consumed (if appropriate), but later writes will @emph{not} produce a
2443 BOM. Similarly, if the user writes first, then later reads will
2444 @emph{not} consume a BOM.
2447 For ports that do not support seeking (e.g. pipes, sockets, and
2448 terminals), the input and output streams are considered
2449 @emph{independent} for purposes of BOM handling: the first read will
2450 consume a BOM (if appropriate), and the first write will @emph{also}
2451 produce a BOM (if appropriate). However, the input and output streams
2452 will always use the same byte order.
2455 Seeks to the beginning of a file will set the ``start of stream'' flags.
2456 Therefore, a subsequent textual read or write will consume or produce a
2457 BOM. However, unlike @code{set-port-encoding!}, if a byte order had
2458 already been chosen for the port, it will remain in effect after a seek,
2459 and cannot be changed by the presence of a BOM. Seeks anywhere other
2460 than the beginning of a file clear the ``start of stream'' flags.
2464 @c TeX-master: "guile.texi"