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).

       allbox;  lb  lb  lb  l  l  l.   Interface Attribute Value  T{  perror()
       T}   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 4.16 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)