perror (3)
Leading comments
Copyright (c) 1994 Michael Haardt (michael@moria.de), 1994-06-04
Copyright (c) 1995 Michael Haardt
(michael@cantor.informatik.rwth-aachen.de), 1995-03-16
Copyright (c) 1996 Andries Brouwer (aeb@cwi.nl), 1996-01-13
%%%LICENSE_START(GPLv2+_DOC_FULL)
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The G...
NAME
perror - print a system error messageSYNOPSIS
#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: _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 function.First (if s is not NULL and *s is not a null byte (aq\0aq)), 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.
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 sysme 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
For an explanation of the terms used in this section, see attributes(7).| Interface | Attribute | Value |
| perror() | 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.