[code]umask function

If we try, using either open or creat, to create a file that already exists, the file's access permission bits are not changed. We can verify this by running the program from :

     $ rm foo bar               delete the files in case they already exist
     $ date > foo               create them with some data
     $ date > bar
     $ chmod a-r foo bar             turn off all read permissions
     $ ls -l foo bar                 verify their permissions
     --w-------   1 sar     29 Feb 5 14:25 bar
     --w-------   1 sar     29 Feb 5 14:25 foo
     $ ./a.out                       run program from 
     $ ls -l foo bar                 check permissions and sizes
     --w-------   1 sar     0 Feb   5 14:26 bar
     --w-------   1 sar     0 Feb   5 14:26 foo

Note that the permissions didn't change but that the files were truncated.

/*================================================================

mode_t umask( mode_t cmode) function stes the file mode creation

mask for the process and returns the previous value.


==============================================================*/





#include<fcntl.h>
#include<stdio.h>

#define RWRWRW ( S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH )
int main( int argc , char *argv[])
{
   struct stat statbuff;
   umask(0);
   if(creat( "foo" ,RWRWRW)<0 ){
      perror( "create function failed!" );
   }
   umask( S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH );
   if(creat( "bar" ,RWRWRW )<0){
      perror( "create 2 function failed " );
   }
return 0;
}