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 feature_test_macros(7)):

       sys_errlist, sys_nerr:
           Since glibc 2.19:
           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

       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

       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         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

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.08 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

                                 2019-03-06                        PERROR(3)

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