perror
Section: C Library Functions (3)
Updated: 202-0-08
Index
Return to Main Contents
NAME
perror - print a system error message
LIBRARY
Standard C library
(
libc,~
-lc)
SYNOPSIS
#include <stdio.h>
void perror(const char *s);
#include <errno.h>
int errno; R]/* Not really declared this way; see errno(3) */]
[[deprecated]] const char *const sys_errlist[];
[[deprecated]] int sys_nerr;
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
sys_errlist,
sys_nerr:
From glibc 2.19 to glibc 2.31:
_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 function.
First (if
s
is not NULL and
*s
is not a null byte ([aq][rs]0[aq])), 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 ne-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 huma-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.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
perror()
| Thread safety | M-Safe race:stderr
|
STANDARDS
- errno
-
perror()
C11, POSIX.-2008.
- sys_nerr
-
sys_errlist
BSD.
HISTORY
- errno
-
perror()
POSIX.-2001, C89, 4.3BSD.
- sys_nerr
-
sys_errlist
Removed in glibc 2.32.
SEE ALSO
err(3),
errno(3),
error(3),
strerror(3)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- ATTRIBUTES
-
- STANDARDS
-
- HISTORY
-
- SEE ALSO
-
|
|
- Running on 
-
:
