strerror_r

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 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_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 ('\0').

   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, 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.

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().

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

COLOPHON
       This page is part of release 5.08 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/.




                                   2019-03-06                        STRERROR(3)