STRERROR(3)						     Linux Programmer's Manual						       STRERROR(3)

NAME

       strerror, strerror_r, strerror_l - 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 */

       char *strerror_l(int errnum, locale_t locale);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       strerror_r():
	   The XSI-compliant version is provided if:
	   (_POSIX_C_SOURCE >= 200112L) && !  _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  be  "Invalid argument".)  This string must not be modified by the application, but may be modified by a subsequent call to strerror()
       or strerror_l().  No other library function, including perror(3), will modify this string.

   strerror_r()
       The strerror_r() function is similar to strerror(), but is thread safe.	This function is available in two versions: an XSI-compliant  ver-
       sion  specified in POSIX.1-2001 (available since glibc 2.3.4, but not POSIX-compliant until glibc 2.13), and a GNU-specific version (avail-
       able 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_C_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 ('').

   strerror_l()
       strerror_l() is like strerror(), but maps errnum to a locale-dependent error message in the locale specified by locale.	 The  behavior	of
       strerror_l() is undefined if locale is the special locale object LC_GLOBAL_LOCALE or is not a valid locale object handle.

RETURN VALUE

       The  strerror(),  strerror_l(), 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.

       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).

       POSIX.1-2001  and  POSIX.1-2008	require  that  a successful call to strerror() or strerror_l() 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.

ERRORS

       EINVAL The value of errnum is not a valid error number.

       ERANGE Insufficient storage was supplied to contain the error description string.

VERSIONS

       The strerror_l() function first appeared in glibc 2.6.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       +---------------+---------------+-------------------------+
       |Interface      | Attribute     | Value			 |
       +---------------+---------------+-------------------------+
       |strerror()     | Thread safety | MT-Unsafe race:strerror |
       +---------------+---------------+-------------------------+
       |strerror_r(),  | Thread safety | MT-Safe		 |
       |strerror_l()   |	       |			 |
       +---------------+---------------+-------------------------+
CONFORMING TO

       strerror() is specified by POSIX.1-2001, POSIX.1-2008, C89, and C99.  strerror_r() is specified by POSIX.1-2001 and POSIX.1-2008.

       strerror_l() is specified in POSIX.1-2008.

       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, str-
       error() 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.

NOTES

       The GNU C Library uses a buffer of 1024 characters for strerror().  This buffer size therefore should be  sufficient  to  avoid	an  ERANGE
       error when calling strerror_r() and strerror_l().

SEE ALSO

       err(3), errno(3), error(3), perror(3), strsignal(3), locale(7)

COLOPHON

       This  page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

								    2017-09-15							       STRERROR(3)