NAME
perror(), strerror(), errno, sys_errlist, sys_nerr — system error messages
SYNOPSIS
#include <stdio.h>
void perror(const char *s);
#include <string.h>
char *strerror(int errnum);
#include <errno.h>
extern char *sys_errlist[];
extern int sys_nerr;
Obsolescent Interface
#include <string.h>
int strerror_r(int errnum, char *buffer, int buflen);
DESCRIPTION
perror()
writes a language-dependent message to the standard error output,
describing the last error encountered during a call
to a system or library function.
The argument string
s
is printed first, followed by a colon, a blank,
the message, and a new-line.
To be most useful, the argument string should include the name
of the program that incurred the error.
The error number is taken from the symbol
errno,
which is set when errors occur but not cleared when
non-erroneous calls are made.
The contents of the message is identical to those returned by the
strerror()
function with
errno
as the argument.
If given a
NULL
string, the
perror()
function prints only the message and a new-line.
To simplify variant formatting of messages,
the
strerror()
function and the
sys_errlist
array of message strings are provided.
The
strerror()
function maps the error number in
errnum
to a language-dependent error message string
and returns a pointer to the string.
The message string is returned without a new-line.
errno
can be used as an index into
sys_errlist
to get an untranslated message string without the new-line.
sys_nerr
is the largest message number provided for in the table;
it should be checked because new error codes
might be added to the system before they are added to the table.
strerror()
must be used to retrieve messages when translations are desired.
Obsolescent Interface
strerror_r()
handles system error messages.
APPLICATION USAGE
perror()
and
strerror()
are thread-safe. These interfaces are not async-cancel-safe.
A cancellation point may occur when a thread is executing
perror()
or
strerror().
EXTERNAL INFLUENCES
Environment Variables
The language of the message returned by
strerror()
and printed by
perror()
is specified by the
LANG
environment variable.
If the language-dependent message is not available, or if
LANG
is not set or is set to the empty string,
the default version of the message associated with the "C" language (see
lang(5))
is used.
International Code Set Support
Single- and multi-byte character code sets are supported.
RETURN VALUE
perror()
returns no value.
If the
errnum
message number is valid,
strerror()
returns a pointer to a language-dependent message string.
The array pointed to should not be modified by the program,
and might be overwritten by a subsequent call to the function.
If a valid
errnum
message number does not have a corresponding language-dependent message,
strerror()
uses
errnum
as an index into
sys_errlist
to get the message string.
If the
errnum
message number is invalid,
strerror()
returns a pointer to a
NULL
string.
WARNINGS
The return value for
strerror()
points to data whose content is overwritten by subsequent calls to
strerror()
from the same thread.
strerror_r()
is an obsolescent interface supported only for compatibility with
existing DCE applications. New multithreaded applications should use
strerror().
STANDARDS CONFORMANCE
perror(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C
strerror(): AES, SVID3, XPG3, XPG4, ANSI C
sys_errlist(): SVID2, SVID3, XPG2
sys_nerr(): SVID2, SVID3, XPG2
