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

       strerror,  strerror_r, strerror_l - return string describing error num-

       #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  lan-
       guage.   (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 fea-
       ture test macros settings shown in the SYNOPSIS; otherwise the GNU-spe-
       cific  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 str-
       error_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 str-
       error_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() func-
       tions 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 er-
       ror, 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

       POSIX.1-2001 and POSIX.1-2008 require that a successful  call  to  str-
       error()  or  strerror_l()  shall  leave errno unchanged, and note that,
       since no function return value is reserved to indicate an error, an ap-
       plication  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  descrip-
              tion string.

       The strerror_l() function first appeared in glibc 2.6.

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

       |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  func-
       tion  result in the event of an error.  On some systems, strerror() re-
       turns 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.

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

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

       This  page  is  part of release 5.05 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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