creat system call fail to set permissions

Question

I need to use creat system call to create file (it is used in legacy code and I'm not allowed to change this; example below is simplified one but the problem is just the same). I have the following code:

#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main() 
{
    umask(0);
    int hndl = creat("abc.dat", S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP); // == 0660
    close(hndl);
}

File is created as expected (I checked the timestamp also), but the permissions are different from 0660:

$ gcc creat.c && ./a.out && ll | grep abc
-rwx---r-x 1 ulysses ulysses     0 May    7 19:42 abc.dat*

which are 0705. I tried to use 0660 literally and had the same result. Am I missing something?

Answer 1

Your code looks correct and should do what you want. You should check whether your program actually did create the file: if it did exist already, creat() would succeed without error and update the timestamp, but not change the permissions.