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

NAME
       strerror, strerrorname_np, strerrordesc_np, strerror_r, strerror_l - return string describing error number

SYNOPSIS
       #include <string.h>

       char *strerror(int errnum);
       const char *strerrorname_np(int errnum);
       const char *strerrordesc_np(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)):

       strerrorname_np(), strerrordesc_np():
           _GNU_SOURCE

       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.

       Like strerror(), the strerrordesc_np() function returns a pointer to a string that describes the error code passed in the argument errnum,  with  the  difference
       that the returned string is not translated according to the current locale.

       The strerrorname_np() function returns a pointer to a string containing the name of the error code passed in the argument errnum.  For example, given EPERM as an
       argument, this function returns a pointer to the string "EPERM".

   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  unde‐
       fined 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.

       On success, strerrorname_np() and strerrordesc_np() return the appropriate error description string.  If errnum is an invalid error number, these  functions  re‐
       turn NULL.

       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 af‐
       ter 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.

       The strerrorname_np() and strerrordesc_np() functions first appeared in glibc 2.32.

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

       β”Œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”
       β”‚Interface                            β”‚ Attribute     β”‚ Value                                                                                                    β”‚
       β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€
       β”‚strerror()                           β”‚ Thread safety β”‚ MT-Unsafe race:strerror                                                                                  β”‚
       β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€
       β”‚strerrorname_np(), strerrordesc_np() β”‚ Thread safety β”‚ MT-Safe                                                                                                  β”‚
       β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€
       β”‚strerror_r(), strerror_l()           β”‚ Thread safety β”‚ MT-Safe                                                                                                  β”‚
       β””β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”˜

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 functions strerror_r(), strerrorname_np(), and strerrordesc_np() are nonstandard extensions.

       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  str‐
       error_r().

       strerrorname_np() and strerrordesc_np() are thread-safe and async-signal-safe.

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

                                                                               2021-03-22                                                                    STRERROR(3)