umask.md

title	description	ms.date	api_name	api_location	api_type	topic_type	f1_keywords	helpviewer_keywords	ms.assetid
_umask	API reference for _umask; which sets the default file-permission mask.	4/2/2020	_umask _o__umask	msvcrt.dll msvcr80.dll msvcr90.dll msvcr100.dll msvcr100_clr0400.dll msvcr110.dll msvcr110_clr0400.dll msvcr120.dll msvcr120_clr0400.dll ucrtbase.dll api-ms-win-crt-filesystem-l1-1-0.dll	DLLExport	apiref	CORECRT_IO/_umask _umask	masks, file-permission-setting _umask function masks umask function file permissions [C++] files [C++], permission settings for	5e9a13ba-5321-4536-8721-6afb6f4c8483

_umask

Sets the default file-permission mask. For a more secure version of this function, see _umask_s .

Syntax

int_umask( intpmode );

Parameters

pmode
Default permission setting.

Return value

_umask returns the previous value of pmode. There's 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 isn't 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:

pmode	Description
_S_IWRITE	Writing permitted.
_S_IREAD	Reading permitted.
**`_S_IREAD	_S_IWRITE`**

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

If pmode isn't a combination of one of the manifest constants or incorporates an alternate set of constants, the function ignores them.

By default, this function's global state is scoped to the application. To change it, see Global state in the CRT.

Requirements

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

For more compatibility information, see Compatibility.

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>intmain( void ) { intoldmask; /* Create read-only files: */oldmask=_umask( _S_IWRITE ); // C4996// Note: _umask is deprecated; consider using _umask_s insteadprintf( "Oldmask = 0x%.4x\n", oldmask ); }

Oldmask = 0x0000 

See also

File handling
Low-level I/O
_chmod, _wchmod
_creat, _wcreat
_mkdir, _wmkdir
_open, _wopen