| NAME | SYNOPSIS | DESCRIPTION | CONFORMING TO | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
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 *sys_errlist[];
int sys_nerr;
int errno;
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
sys_errlist, sys_nerr: _BSD_SOURCE
The routine perror() produces a message on the standard error output,
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 the message and a new-line.
To be of most use, the argument string should include the name of the
function that incurred the error. The error number is taken from the
external variable errno, which is set when errors occur but not
cleared when successful calls are made.
The global error list sys_errlist[] 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.
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
library 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.
The function perror() and the external errno (see errno(3)) conform
to C89, C99, 4.3BSD, POSIX.1-2001. The externals sys_nerr and
sys_errlist conform to BSD.
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 3.51 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
2012-04-17 PERROR(3)
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