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 *
sys_errlist
[];
int
sys_nerr
;
int
errno
;
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
sys_errlist,
sys_nerr: _BSD_SOURCE
DESCRIPTION
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.
CONFORMING TO
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.
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 3.53 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/.