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
   function.

   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
   deprecated; 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
   followed 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 4.09 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)

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