c - linux mkdir function can't authorize full permission -

i testing mkdir function create new directory:

folder =  mkdir("./linux", 511); 

or

 folder = mkdir("./linux", 0777); 

or

folder = mkdir("./linux", s_irwxu | s_irwxg | s_irwxo); 

as can see, try authorize full permission directory here's comes ls -l | grep linux:

drwxr-xr-x 2 manuzhang manuzhang 4096 2012-01-04 06:53 linux 

why can't authorize write permission group , others?

updates:
weird thing, guys told me tried umask. works either umask(s_iwgrp) or umask(s_iwoth) fails umask(s_iwgrp | s_iwoth), ideas?

from man 2 mkdir:

the argument mode specifies permissions use. modified process's umask in usual way: permissions of created directory (mode & ~umask & 0777).

i suggest @ umask - set 0022. try chmod post-mkdir.