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NAME | SYNOPSIS | DESCRIPTION | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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PERROR(3) Linux Programmer's Manual PERROR(3)
perror - print a system error message
#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
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.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────┬───────────────┬─────────────────────┐
│Interface │ Attribute │ Value │
├──────────┼───────────────┼─────────────────────┤
│perror() │ Thread safety │ MT-Safe race:stderr │
└──────────┴───────────────┴─────────────────────┘
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.
The externals sys_nerr and sys_errlist are defined by glibc, but in
<stdio.h>.
err(3), errno(3), error(3), strerror(3)
This page is part of release 4.15 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)
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)
Copyright and license for this manual page
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