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41d8e8b2 TTN |
1 | ttn 2004-05-09 |
2 | ||
3 | The exit value of a program returning to the shell on unixoid systems is | |
4 | typically 0 for success, and non-0 (such as 1) for failure. For vms it is | |
5 | odd (1,3,5...) for success, even (0,2,4...) for failure. | |
6 | ||
7 | This holds from the point of view of the "shell" (in quotes because vms has a | |
8 | different dispatch model that is not explained further here). | |
9 | ||
10 | From the point of view of the program, nowadays stdlib.h on both type of | |
11 | systems provides macros `EXIT_SUCCESS' and `EXIT_FAILURE' that should DTRT. | |
12 | ||
9b053e76 | 13 | NB: The numerical values of these macros DO NOT need to fulfill the exit |
41d8e8b2 TTN |
14 | value requirements outlined in the first paragraph! That is the job of the |
15 | `exit' function. Thus, this kind of construct shows misunderstanding: | |
16 | ||
17 | #ifdef VMS | |
18 | exit (1); | |
19 | #else | |
20 | exit (0); | |
21 | #endif | |
22 | ||
23 | Values aside from EXIT_SUCCESS and EXIT_FAILURE are tricky. | |
f87899eb TTN |
24 | |
25 | ||
26 | ||
27 | ttn 2004-05-12 | |
28 | ||
29 | Values aside from EXIT_SUCCESS and EXIT_FAILURE can be used to indicate | |
30 | finer gradations of failure. If this is the only information available | |
31 | to the caller, clamping such values to EXIT_FAILURE loses information. | |
32 | If there are other ways to indicate the problem to the caller (such as | |
33 | a message to stderr) it may be ok to clamp. In all cases, it is the | |
34 | relationship between the program and its caller that must be examined. | |
35 | [Insert ZAMM quote here.] |