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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 4.15 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/.
                                  2017-09-15                         PERROR(3)