man_3_perror.txt

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 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 in‐
       curred the error.

       The  global error list sys_errlist[], which can be indexed by errno, can be used to ob‐
       tain 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 suc‐
       ceeds, 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 5.05 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/.

                                          2019-03-06                                 PERROR(3)