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 * const sys_errlist[];
       int sys_nerr;
       int errno;	/* Not really declared this way; see errno(3) */

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

       sys_errlist, sys_nerr:
	   Since glibc 2.19:
	       _DEFAULT_SOURCE
	   Glibc 2.19 and earlier:
	       _BSD_SOURCE

DESCRIPTION
       The  perror()  function produces a message on standard error describing
       the last error encountered during a call to a system or	library	 func-
       tion.

       First (if s is not NULL and *s is not a null byte ('\0')), the argument
       string s is printed, followed by a colon and a blank.   Then  an	 error
       message corresponding to the current value of errno and a new-line.

       To  be  of most use, the argument string should include the name of the
       function that incurred the error.

       The global error list sys_errlist[], which can be indexed by errno, can
       be  used	 to obtain the error message without the newline.  The largest
       message number 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[].  The use of sys_errlist[] is nowadays dep-
       recated; use strerror(3) instead

       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 system call or library
       function 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  fol-
       lowed by a call to perror(), the value of errno should be saved.

ATTRIBUTES
       For   an	  explanation	of   the  terms	 used  in  this	 section,  see
       attributes(7).

       +----------+---------------+---------------------+
       |Interface | Attribute	  | Value		|
       +----------+---------------+---------------------+
       |perror()  | Thread safety | MT-Safe race:stderr |
       +----------+---------------+---------------------+

CONFORMING TO
       perror(), errno: POSIX.1-2001, POSIX.1-2008, C89, C99, 4.3BSD.

       The externals sys_nerr and sys_errlist derive from  BSD,	 but  are  not
       specified in POSIX.1.

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 4.10 of the Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       https://www.kernel.org/doc/man-pages/.



				  2016-03-15			     PERROR(3)