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)