File Permission Problems

File Permission-general Linux technology-Linux programming and kernel information. For more information, see the following section. # Include
# Include
# Include

Int main ()
{
Struct stat buf;

If (stat ("./test.txt", & buf) =-1 ){
Perror ("fail to stat ");
Exit (1 );
}

If (buf. st_mode & S_IRGRP! = 0)
Printf ("user of the group can read \ n ");
Else
Printf ("user of the group can't read \ n ");

Return 0;
}
The program running result is: user of the grouop can't read
However, when you use the ls-l test.txt command on the terminal
-Rwxr ----- 1 wl 12 test.txt
The user of the group can read should be displayed.
Why?