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

       strerror, strerror_r, strerror_l - return string describing error

       #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.

       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

       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.

       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.

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

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

       The strerror_l() function first appeared in glibc 2.6.

       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()   │               │                         │
       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.

       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().

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

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       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

                                  2019-03-06                       STRERROR(3)