NAME
perror,
strerror,
strerror_r,
sys_errlist,
sys_nerr —
system error
messages
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
void
perror(
const char
*string);
#include <errno.h>
extern const char * const sys_errlist[];
extern const int sys_nerr;
#include <string.h>
char *
strerror(
int
errnum);
int
strerror_r(
int
errnum,
char
*strerrbuf,
size_t
buflen);
DESCRIPTION
The
strerror(),
strerror_r(), and
perror() functions look up the language-dependent error
message string corresponding to an error number.
The
strerror() function accepts an error number argument
errnum and returns a pointer to the corresponding
message string.
The
strerror_r() function renders the same result into
strerrbuf for a maximum of
buflen
characters and returns 0 upon success.
The
perror() function finds the error message corresponding to
the current value of the global variable
errno
(
intro(2)) and writes it,
followed by a newline, to the standard error file descriptor. If the argument
string is non-
NULL
and does not
point to the nul character, this string is prepended to the message string and
separated from it by a colon and space
(“
:
”); otherwise, only the error
message string is printed. Note that in most cases the
err(3) and
warn(3) family of functions is
preferable to
perror(); they are more flexible and also
print the program name.
If the error number is not recognized, these functions pass an error message
string containing “
Unknown error:
”
followed by the error number in decimal. To warn about this,
strerror() sets
errno
to
EINVAL
, and
strerror_r() returns
EINVAL
. Error numbers recognized by this
implementation fall in the range 0 <
errnum <
sys_nerr.
If insufficient storage is provided in
strerrbuf (as
specified in
buflen) to contain the error string,
strerror_r() returns
ERANGE
and
strerrbuf will contain an error message that has been
truncated and
NUL
terminated to fit the length
specified by
buflen.
The message strings can be accessed directly using the external array
sys_errlist. The external value
sys_nerr contains a count of the messages in
sys_errlist. The use of these variables is deprecated;
strerror() or
strerror_r() should be used
instead.
SEE ALSO
intro(2),
err(3),
psignal(3),
warn(3)
STANDARDS
The
perror() and
strerror() functions
conform to
ISO/IEC 9899:1999
(“ISO C99”). The
strerror_r()
function conforms to
IEEE Std 1003.1-2001
(“POSIX.1”).
HISTORY
The
perror() function first appeared in
Version 4 AT&T UNIX. The
strerror() function first appeared in
4.3BSD-Reno. The
strerror_r()
function first appeared in
NetBSD 4.0.
BUGS
For unknown error numbers, the
strerror() function will return
its result in a static buffer which may be overwritten by subsequent calls.
The return type for
strerror() is missing a type-qualifier; it
should actually be
const char *.
Programs that use the deprecated
sys_errlist variable
often fail to compile because they declare it inconsistently.