strerror, _strerror, _wcserror, __wcserror

Gets a system error message string (strerror, _wcserror) or formats a user-supplied error message string (_strerror, __wcserror). More secure versions of these functions are available; see strerror_s, _strerror_s, _wcserror_s, __wcserror_s.

char *strerror(
   int errnum 
char *_strerror(
   const char *strErrMsg 
wchar_t * _wcserror(
   int errnum 
wchar_t * __wcserror(
   const wchar_t *strErrMsg 


Error number.


User-supplied message.

All of these functions return a pointer to the error-message string. Subsequent calls can overwrite the string.

The strerror function maps errnum to an error-message string and returns a pointer to the string. Neither strerror nor _strerror actually prints the message: For that, you have to call an output function such as fprintf:

if (( _access( "datafile",2 )) == -1 )
   fprintf( stderr, _strerror(NULL) );

If strErrMsg is passed as NULL, _strerror returns a pointer to a string that contains the system error message for the last library call that produced an error. The error-message string is terminated by the newline character ('\n'). If strErrMsg is not equal to NULL, then _strerror returns a pointer to a string that contains (in order) your string message, a colon, a space, the system error message for the last library call that produces an error, and a newline character. Your string message can be, at most, 94 characters long.

The actual error number for _strerror is stored in the variable errno. To produce accurate results, call _strerror immediately after a library routine returns with an error. Otherwise, subsequent calls to strerror or _strerror can overwrite the errno value.

_wcserror and __wcserror are wide-character versions of strerror and _strerror, respectively.

_strerror, _wcserror, and __wcserror are not part of the ANSI definition; they are Microsoft extensions and we recommend that you do not use them where you want portable code. For ANSI compatibility, use strerror instead.

To get error strings, we recommend strerror or _wcserror instead of the deprecated macros _sys_errlist and _sys_nerr and the deprecated internal functions __sys_errlist and __sys_nerr.

Generic-Text Routine Mappings

TCHAR.H routine

_UNICODE & _MBCS not defined

_MBCS defined

_UNICODE defined






Required header





_wcserror , __wcserror


For additional compatibility information, see Compatibility.

See the example for perror.