perror, _wperror

Article
12/18/2017

The latest version of this topic can be found at perror, _wperror.

Print an error message.

Syntax

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

Parameters

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 the Windows operating system, 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 the Windows operating system. perror prints an empty string for any errno value not used by these platforms.

Requirements

Routine	Required header
`perror`	<stdio.h> or <stdlib.h>
`_wperror`	<stdio.h> or <wchar.h>

For additional compatibility information, see Compatibility in the Introduction.

Libraries

All versions of the C run-time libraries.

Example

// crt_perror.c  
// compile with: /W3  
/* 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>  
#include <share.h>  
  
int main( void )  
{  
   int  fh;  
  
   if( _sopen_s( &fh, "NOSUCHF.ILE", _O_RDONLY, _SH_DENYNO, 0 ) != 0 )  
   {  
      /* Three ways to create error message: */  
      perror( "perror says open failed" );  
      printf( "strerror says open failed: %s\n",  
         strerror( errno ) ); // C4996  
      printf( _strerror( "_strerror says open failed" ) ); // C4996  
      // Note: strerror and _strerror are deprecated; consider  
      // using strerror_s and _strerror_s instead.  
   }  
   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

.NET Framework Equivalent

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.