NAME¶
strerror, strerror_r - return string describing error number
SYNOPSIS¶
#include <string.h>
char *strerror(int errnum);
int strerror_r(int errnum, char *buf, size_t buflen);
/* XSI-compliant */
char *strerror_r(int errnum, char *buf, size_t buflen);
/* GNU-specific */
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
The XSI-compliant version of
strerror_r() is provided if:
(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
&& ! _GNU_SOURCE
Otherwise, the GNU-specific version is provided.
DESCRIPTION¶
The
strerror() function returns a pointer to a string that describes the
error code passed in the argument
errnum, possibly using the
LC_MESSAGES part of the current locale to select the appropriate
language. (For example, if
errnum is
EINVAL, the returned
description will "Invalid argument".) This string must not be
modified by the application, but may be modified by a subsequent call to
strerror(). No library function, including
perror(3), will
modify this string.
The
strerror_r() function is similar to
strerror(), but is thread
safe. This function is available in two versions: an XSI-compliant version
specified in POSIX.1-2001 (available since glibc 2.3.4, but not
POSIX-compliant until glibc 2.13), and a GNU-specific version (available since
glibc 2.0). The XSI-compliant version is provided with the feature test macros
settings shown in the SYNOPSIS; otherwise the GNU-specific version is
provided. If no feature test macros are explicitly defined, then (since glibc
2.4)
_POSIX_SOURCE is defined by default with the value 200112L, so
that the XSI-compliant version of
strerror_r() is provided by default.
The XSI-compliant
strerror_r() is preferred for portable applications. It
returns the error string in the user-supplied buffer
buf of length
buflen.
The GNU-specific
strerror_r() returns a pointer to a string containing
the error message. This may be either a pointer to a string that the function
stores in
buf, or a pointer to some (immutable) static string (in which
case
buf is unused). If the function stores a string in
buf,
then at most
buflen bytes are stored (the string may be truncated if
buflen is too small and
errnum is unknown). The string always
includes a terminating null byte.
RETURN VALUE¶
The
strerror() and the GNU-specific
strerror_r() functions return
the appropriate error description string, or an "Unknown error nnn"
message if the error number is unknown.
POSIX.1-2001 and POSIX.1-2008 require that a successful call to
strerror(3) shall leave
errno unchanged, and note that, since no
function return value is reserved to indicate an error, an application that
wishes to check for errors should initialize
errno to zero before the
call, and then check
errno after the call.
The XSI-compliant
strerror_r() function returns 0 on success. On error, a
(positive) error number is returned (since glibc 2.13), or -1 is returned and
errno is set to indicate the error (glibc versions before 2.13).
ERRORS¶
- EINVAL
- The value of errnum is not a valid error
number.
- ERANGE
- Insufficient storage was supplied to contain the error
description string.
strerror() is specified by POSIX.1-2001, C89, C99.
strerror_r() is
specified by POSIX.1-2001.
The GNU-specific
strerror_r() function is a nonstandard extension.
POSIX.1-2001 permits
strerror() to set
errno if the call
encounters an error, but does not specify what value should be returned as the
function result in the event of an error. On some systems,
strerror()
returns NULL if the error number is unknown. On other systems,
strerror() returns a string something like "Error nnn
occurred" and sets
errno to
EINVAL if the error number is
unknown. C99 and POSIX.1-2008 require the return value to be non-NULL.
SEE ALSO¶
err(3),
errno(3),
error(3),
perror(3),
strsignal(3)
COLOPHON¶
This page is part of release 3.44 of the Linux
man-pages project. A
description of the project, and information about reporting bugs, can be found
at
http://www.kernel.org/doc/man-pages/.