_chmod, _wchmod

Visual Studio 6.0

Change the file-permission settings.

int _chmod( const char *filename, int pmode );

int _wchmod( const wchar_t *filename, int pmode );

Routine Required Header Optional Headers Compatibility
_chmod <io.h> <sys/types.h>, <sys/stat.h>, <errno.h> Win 95, Win NT
_wchmod <io.h> or <wchar.h> <sys/types.h>, <sys/stat.h>, <errno.h> Win NT

For additional compatibility information, see Compatibility in the Introduction.


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

Each of these functions returns 0 if the permission setting is successfully changed. A return value of –1 indicates that the specified file could not be found, in which case errno is set to ENOENT.



Name of existing file


Permission setting for file


The _chmod function changes the permission setting of the file specified by filename. The permission setting controls read and write access to the file. The integer expression pmode contains one or both of the following manifest constants, defined in SYS\STAT.H:


Writing permitted


Reading permitted


Reading and writing permitted

Any other values for pmode are ignored. When both constants are given, they are joined with the bitwise-OR operator ( | ). If write permission is not given, the file is read-only. Note that all files are always readable; it is not possible to give write-only permission. Thus the modes _S_IWRITE and _S_IREAD | _S_IWRITE are equivalent.

_wchmod is a wide-character version of _chmod; the filename argument to _wchmod is a wide-character string. _wchmod and _chmod behave identically otherwise.

Generic-Text Routine Mappings

TCHAR.H Routine _UNICODE & _MBCS Not Defined _MBCS Defined _UNICODE Defined
_tchmod _chmod _chmod _wchmod


/* CHMOD.C: This program uses _chmod to
 * change the mode of a file to read-only.
 * It then attempts to modify the file.

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

void main( void )
   /* Make file read-only: */
   if( _chmod( "CHMOD.C", _S_IREAD ) == -1 )
      perror( "File not found\n" );
      printf( "Mode changed to read-only\n" );
   system( "echo /* End of file */ >> CHMOD.C" );

   /* Change back to read/write: */
   if( _chmod( "CHMOD.C", _S_IWRITE ) == -1 )
      perror( "File not found\n" );
      printf( "Mode changed to read/write\n" );
   system( "echo /* End of file */ >> CHMOD.C" );


Mode changed to read-only
Access is denied
Mode changed to read/write

File Handling Routines

See Also   _access, _creat, _fstat, _open, _stat