perror(3) Library Functions Manual perror(3)
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; /* 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 func-
tion.
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 dep-
recated; 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 fol-
lowed by a call to perror(), the value of errno should be saved.
VERSIONS
Since glibc 2.32, the declarations of sys_errlist and sys_nerr are no
longer exposed by <stdio.h>.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌────────────────────────────────┬───────────────┬─────────────────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────┼───────────────┼─────────────────────┤
│perror() │ Thread safety │ MT-Safe race:stderr │
└────────────────────────────────┴───────────────┴─────────────────────┘
STANDARDS
perror(), errno: POSIX.1-2001, POSIX.1-2008, C99, 4.3BSD.
The externals sys_nerr and sys_errlist derive from BSD, but are not
specified in POSIX.1.
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)
Linux man-pages 6.03 2023-02-05 perror(3)
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