strerror, _strerror

Get a system error message (strerror) or prints a user-supplied error message (_strerror).

char *strerror( int errnum );

char *_strerror( const char *strErrMsg );

For additional compatibility information, see Compatibility in the Introduction.

Libraries

Return Value

strerror and _strerror return a pointer to the error-message string. Subsequent calls to strerror or _strerror can overwrite the string.

Parameters

errnum

Error number

strErrMsg

User-supplied message

Remarks

The strerror function maps errnum to an error-message string, returning a pointer to the string. Neither strerror nor _strerror actually prints the message: For that, you need 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 containing 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 containing (in order) your string message, a colon, a space, the system error message for the last library call producing an error, and a newline character. Your string message can be, at most, 94 bytes long.

The actual error number for _strerror is stored in the variable errno. The system error messages are accessed through the variable _sys_errlist, which is an array of messages ordered by error number. _strerror accesses the appropriate error message by using the errno value as an index to the variable _sys_errlist. The value of the variable _sys_nerr is defined as the maximum number of elements in the _sys_errlist array. 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.

_strerror is not part of the ANSI definition but is instead a Microsoft extension to it. Do not use it where portability is desired; for ANSI compatibility, use strerror instead.

Example

/* PERROR.C: This program attempts to open a file named
 * NOSUCHF.ILE. Because this file probably doesn't exist,
 * an error message is displayed. The same message is
 * created using perror, strerror, and _strerror.
 */

#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <io.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

void main( void )
{
   int  fh;

   if( (fh = _open( "NOSUCHF.ILE", _O_RDONLY )) == -1 )
   {
      /* Three ways to create error message: */
      perror( "perror says open failed" );
      printf( "strerror says open failed: %s\n", strerror( errno ) );
      printf( _strerror( "_strerror says open failed" ) );
   }
   else
   {
      printf( "open succeeded on input file\n" );
      _close( fh );
   }
}

Output

perror says open failed: No such file or directory

strerror says open failed: No such file or directory
_strerror says open failed: No such file or directory

String Manipulation Routines

See Also   clearerr, ferror, perror