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
: From glibc 2.19 to 2.31:
_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.
Since glibc version 2.32, the declarations of sys_errlist
and sys_nerr
are no longer exposed by
<stdio.h>
.
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>
.
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https://www.kernel.org/doc/man-pages/.