_umask

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06/05/2017

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

Syntax

int _umask(  
   int pmode   
);

Parameters

pmode
Default permission setting.

Return Value

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

Remarks

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.

Requirements

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

For additional compatibility information, see Compatibility in the Introduction.

Libraries

All versions of the C run-time libraries.

Example

// 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

.NET Framework Equivalent

System::IO::File::SetAttributes

共用方式為