perror(3) — Linux manual page


PERROR(3)               Linux Programmer's Manual              PERROR(3)

NAME         top

       perror - print a system error message

SYNOPSIS         top

       #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

       sys_errlist, sys_nerr:
           From glibc 2.19 to 2.31:
           Glibc 2.19 and earlier:

DESCRIPTION         top

       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.

VERSIONS         top

       Since glibc version 2.32, the declarations of sys_errlist and
       sys_nerr are no longer exposed by <stdio.h>.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

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

CONFORMING TO         top

       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         top

       The externals sys_nerr and sys_errlist are defined by glibc, but
       in <stdio.h>.

SEE ALSO         top

       err(3), errno(3), error(3), strerror(3)

COLOPHON         top

       This page is part of release 5.13 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

                               2021-03-22                      PERROR(3)

Pages that refer to this page: err(3)errno(3)error(3)fmtmsg(3)pmerrstr(3)psignal(3)sd_journal_print(3)stdio(3)strerror(3)