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umask

Header File

io.h, sys\stat.h

Category

Input/output Routines

Prototype

unsigned umask(unsigned mode);

Description

Sets file read/write permission mask.

The umask function sets the access permission mask used by open and creat. Bits that are set in mode will be cleared in the access permission of files subsequently created by open and creat.

The mode can have one of the following values, defined in sys\stat.h:

S_IWRITE | Permission to write
S_IREAD | Permission to read
S_IREAD|S_IWRITE | Permission to read and write

Return Value

The previous value of the mask. There is no error return.

Example

Copy Code

    #include <io.h>
    #include <stdio.h>
    #include <sys\stat.h>
    #define FILENAME "TEST.$$$"
    int main(void)
    {
        unsigned oldmask;
        FILE *f;
        struct stat statbuf;
        /* Cause subsequent files to be created as read-only */
        oldmask = umask(S_IWRITE);
        printf("Old mask = 0x%x\n",oldmask);
        /* Create a zero-length file */
        if ((f = fopen(FILENAME,"w+")) == NULL)
        {
            perror("Unable to create output file");
            return (1);
        }
        fclose(f);
        /* Verify that the file is read-only */
        if (stat(FILENAME,&statbuf) != 0)
        {
            perror("Unable to get information about output file");
            return (1);
        }
        if (statbuf.st_mode & S_IWRITE)
            printf("Error! %s is writable!\n",FILENAME);
        else
            printf("Success! %s is not writable.\n",FILENAME);
        return (0);
    }

Portability

POSIX | Win32 | ANSI C | ANSI C++
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