strerror(3) — Linux manual page


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

NAME         top

       strerror,  strerror_r,  strerror_l  -  return string describing error

SYNOPSIS         top

       #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)):

           The XSI-compliant version is provided if:
           (_POSIX_C_SOURCE >= 200112L) && !  _GNU_SOURCE
           Otherwise, the GNU-specific version is provided.

DESCRIPTION         top

       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.

       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() 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         top

       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         top

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

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

VERSIONS         top

       The strerror_l() function first appeared in glibc 2.6.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface      Attribute     Value                   │
       │strerror()     │ Thread safety │ MT-Unsafe race:strerror │
       │strerror_r(),  │ Thread safety │ MT-Safe                 │
       │strerror_l()   │               │                         │

CONFORMING TO         top

       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         top

       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         top

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

COLOPHON         top

       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

                                 2019-03-06                      STRERROR(3)

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