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perror, _wperror

Print an error message.

void perror(
   const char *string 
);
void _wperror(
   const wchar_t *string 
);

Parameter

string
String message to print.

Remarks

The perror function prints an error message to stderr. _wperror is a wide-character version of _perror; the string argument to _wperror is a wide-character string. _wperror and _perror behave identically otherwise.

Generic-Text Routine Mappings

TCHAR.H routine _UNICODE & _MBCS not defined _MBCS defined _UNICODE defined
_tperror perror perror _wperror

string is printed first, followed by a colon, then by the system error message for the last library call that produced the error, and finally by a newline character. If string is a null pointer or a pointer to a null string, perror prints only the system error message.

The error number is stored in the variable errno (defined in ERRNO.H). The system error messages are accessed through the variable _sys_errlist, which is an array of messages ordered by error number. perror prints the appropriate error message using the errno value as an index to _sys_errlist. The value of the variable _sys_nerr is defined as the maximum number of elements in the _sys_errlist array.

For accurate results, call perror immediately after a library routine returns with an error. Otherwise, subsequent calls can overwrite the errno value.

In Windows 98/Me and Windows NT/2000/XP, some errno values listed in ERRNO.H are unused. These values are reserved for use by the UNIX operating system. See _doserrno, errno, _sys_errlist, and _sys_nerr for a listing of errno values used by Windows 98/Me and Windows NT/2000/XP. perror prints an empty string for any errno value not used by these platforms.

Note   In the Visual C++ implementation of the C run-time library, perror does not write to the same stream as stderr.

Requirements

Routine Required header Compatibility
perror <stdio.h> or <stdlib.h> ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP
_wperror <stdio.h> or <wchar.h> Win 98, Win Me, Win NT, Win 2000, Win XP

For additional compatibility information, see Compatibility in the Introduction.

Libraries

All versions of the C run-time libraries.

Example

// crt_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>

int 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

See Also

Process and Environment Control Routines | clearerr | ferror | strerror | Run-Time Routines and .NET Framework Equivalents

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