redhat man page for perror

PERROR(3)							 Library functions							 PERROR(3)

NAME
       perror - print a system error message

SYNOPSIS
       #include <stdio.h>

       void perror(const char *s);

       #include <errno.h>

       const char *sys_errlist[];
       int sys_nerr;

DESCRIPTION
       The  routine  perror()  produces a message on the standard error output, describing the last error encountered during a call to a system or
       library function.  First (if s is not NULL and *s is not NUL) the argument string s is printed, followed by a colon and a blank.  Then  the
       message and a new-line.

       To be of most use, the argument string should include the name of the function that incurred the error.	The error number is taken from the
       external variable errno, which is set when errors occur but not cleared when non-erroneous calls are made.

       The global error list sys_errlist[] indexed by errno can be used to obtain the error message without the newline.  The largest message num-
       ber provided in the table is sys_nerr -1.  Be careful when directly accessing this list because new error values may not have been added to
       sys_errlist[].

       When a system call fails, it usually returns -1 and sets the variable errno to a value describing what went wrong.  (These  values  can	be
       found  in  <errno.h>.)	Many library functions do likewise.  The function perror() serves to translate this error code into human-readable
       form.  Note that errno is undefined after a successful library call: this call may well change this variable, even though it succeeds,  for
       example	because it internally used some other library function that failed.  Thus, if a failing call is not immediately followed by a call
       to perror, the value of errno should be saved.

CONFORMING TO
       ANSI C, BSD 4.3, POSIX, X/OPEN

SEE ALSO
       strerror(3)

								    2001-12-14								 PERROR(3)