man:sys_nerr
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 func- tion.
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 dep- recated; 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 fol-
lowed 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).
allbox; lb lb lb l l l. Interface Attribute Value T{ perror() T} 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 4.16 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)
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