PERROR(3)						     Linux Programmer's Manual							 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;
       int errno;

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sys_errlist, sys_nerr: _BSD_SOURCE

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 a null byte ('')) 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 successful 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

       The function perror() and the external errno (see errno(3)) conform  to	C89,  C99,  4.3BSD,  POSIX.1-2001.   The  externals  sys_nerr  and
       sys_errlist conform to BSD.

NOTES

       The externals sys_nerr and sys_errlist are defined by glibc, but in <stdio.h>.

SEE ALSO

       err(3), errno(3), error(3), strerror(3)

COLOPHON

       This  page is part of release 3.25 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

								    2007-07-26								 PERROR(3)