Sets the default file-permission mask. A more secure version of this function is available; see _umask_s.


int _umask( int pmode );


Default permission setting.

Return Value

_umask returns the previous value of pmode. There is no error return.


The _umask function sets the file-permission mask of the current process to the mode specified by pmode. The file-permission mask modifies the permission setting of new files created by _creat, _open, or _sopen. If a bit in the mask is 1, the corresponding bit in the file's requested permission value is set to 0 (disallowed). If a bit in the mask is 0, the corresponding bit is left unchanged. The permission setting for a new file is not set until the file is closed for the first time.

The integer expression pmode contains one or both of the following manifest constants, defined in SYS\STAT.H:

_S_IWRITE Writing permitted.
_S_IREAD Reading permitted.
_S_IREAD | _S_IWRITE Reading and writing permitted.

When both constants are given, they are joined with the bitwise-OR operator ( | ). If the pmode argument is _S_IREAD, reading is not allowed (the file is write-only). If the pmode argument is _S_IWRITE, writing is not allowed (the file is read-only). For example, if the write bit is set in the mask, any new files will be read-only. Note that with MS-DOS and the Windows operating systems, all files are readable; it is not possible to give write-only permission. Therefore, setting the read bit with _umask has no effect on the file's modes.

If pmode is not a combination of one of the manifest constants or incorporates an alternate set of constants, the function will simply ignore those.


Routine Required header
_umask <io.h>, <sys/stat.h>, <sys/types.h>

For additional compatibility information, see Compatibility.


All versions of the C run-time libraries.


// crt_umask.c
// compile with: /W3
// This program uses _umask to set
// the file-permission mask so that all future
// files will be created as read-only files.
// It also displays the old mask.
#include <sys/stat.h>
#include <sys/types.h>
#include <io.h>
#include <stdio.h>

int main( void )
   int oldmask;

   /* Create read-only files: */
   oldmask = _umask( _S_IWRITE ); // C4996
   // Note: _umask is deprecated; consider using _umask_s instead
   printf( "Oldmask = 0x%.4x\n", oldmask );
Oldmask = 0x0000

See also

File Handling
Low-Level I/O
_chmod, _wchmod
_creat, _wcreat
_mkdir, _wmkdir
_open, _wopen