Question about perror

[Doug Gwyn]

In article <4573 at oasys.dt.navy.mil> stuart at oasys.dt.navy.mil (Stuart Pearlman) writes:
>Is perror() specified in the ansi C standard?  I avoid using perror()
>after library routines such as fopen() because they can fail for other
>reasons besides the system calls they make failing.  Are any of the
>library functions specified in the standard guaranteed to set errno?
>(Is errno even guaranteed to exist?)  What about posix 1003.1?  Does
>it specify what functions you can call perror() after?

perror() is required for ANSI C conformance.  errno is required, but
only a few of the standard functions (mainly math functions) are
required to set errno (upon certain conditions).  IEEE Std 1003.1
specifies that errno is to be set for error returns from a large
number of functions (mainly those normally implemented on UNIX as
genuine system calls).  The allowable values of errno (<errno.h>
macros) are specified for each function.