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36 lines
1.3 KiB
Plaintext
36 lines
1.3 KiB
Plaintext
ttn 2004-05-09
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The exit value of a program returning to the shell on unixoid systems is
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typically 0 for success, and non-0 (such as 1) for failure. For vms it is
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odd (1,3,5...) for success, even (0,2,4...) for failure.
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This holds from the point of view of the "shell" (in quotes because vms has a
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different dispatch model that is not explained further here).
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From the point of view of the program, nowadays stdlib.h on both type of
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systems provides macros `EXIT_SUCCESS' and `EXIT_FAILURE' that should DTRT.
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NB: The numerical values of these macros DO NOT need to fulfill the the exit
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value requirements outlined in the first paragraph! That is the job of the
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`exit' function. Thus, this kind of construct shows misunderstanding:
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#ifdef VMS
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exit (1);
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#else
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exit (0);
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#endif
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Values aside from EXIT_SUCCESS and EXIT_FAILURE are tricky.
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ttn 2004-05-12
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Values aside from EXIT_SUCCESS and EXIT_FAILURE can be used to indicate
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finer gradations of failure. If this is the only information available
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to the caller, clamping such values to EXIT_FAILURE loses information.
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If there are other ways to indicate the problem to the caller (such as
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a message to stderr) it may be ok to clamp. In all cases, it is the
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relationship between the program and its caller that must be examined.
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[Insert ZAMM quote here.]
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