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Sets the default file-permission mask.

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 argument pmode is a constant expression containing one or both of the manifest constants _S_IREAD and _S_IWRITE, defined in SYS\STAT.H. 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.


Routine Required header Compatibility
_umask <io.h> and <sys/stat.h> and <sys/types.h> Win 98, Win Me, Win NT, Win 2000, Win XP

For additional compatibility information, see Compatibility in the Introduction.


All versions of the C run-time libraries.


// crt_umask.c
/* 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 );
   printf( "Oldmask = 0x%.4x\n", oldmask );


Oldmask = 0x0000

See Also

File Handling Routines | Low-level I/O Routines | _chmod | _creat | _mkdir | _open | Run-Time Routines and .NET Framework Equivalents