Doubt in structure bitfields

[sureshk]

struct date{
         unsigned short int day:5;
         unsigned short int mon:4;
         unsigned short int year:12;
}dt;
dt.day=12;
dt.mon=5;
dt.year=2000;
printf("%d:%d:%d",dt.day,dt.mon,dt.year);

In the above code the members of the structure are bitfields. we are trying to print those values using %d. "%d" is actually used to retrieve an integer of 2 or 4bytes accorind to the wordsize of the CPU, but here it is of 5,4 or 12 'BITS' only how it is retrieving correctly.
Please clarify my doubt.

[Banfa]

Any integer type <= to the size of an int is passed to a function that does not specify the parameter type (which printf doesn't because it has a variable parameter list) as an int

This is why %d works for char, short and int as well as bit fields, they are all passed on the stack as int.

[sureshk]

Thank you verymuch.