Operator sizeof() in C

Question

Consider the program

main()  
{  
 printf("%d %d %d",sizeof('3'),sizeof("3"),sizeof(3));  
}

output from a gcc compiler is:

4 2 4

Why is it so?

Answer 1

Assuming you are running on a 32-bit system:

sizeof a character literal '3' is 4 because character literals are ints in C language (but not C++).

sizeof "3" is 2 because it is an array literal with length 2 (numeral 3 plus NULL terminator).

sizeof literal 3 is 4 because it is an int.

Answer 2

A few points to keep in mind:

1. sizeof isn't a function, it's an operator. It returns the size of a type in units of sizeof char. In other words sizeof char is always 1.
2. '3' is an int
3. "3" is a char[2], the character 3 then the null terminator.
4. 3 is an int

With these the differences are easily explained:

1. an int requires 4 chars of space to hold it
2. char[2] naturally only requires 2 chars