strerror, _strerror

Visual Studio 6.0

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

char *strerror( int errnum );

char *_strerror( const char *strErrMsg );

Routine Required Header Compatibility
strerror <string.h> ANSI, Win 95, Win NT
_strerror <string.h> Win 95, Win NT

For additional compatibility information, see Compatibility in the Introduction.

Libraries

LIBC.LIB Single thread static library, retail version
LIBCMT.LIB Multithread static library, retail version
MSVCRT.LIB Import library for MSVCRT.DLL, retail version

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

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