Why does “sizeof(a ? true : false)” give an output of four bytes?

Question

I have a small piece of code about the sizeof operator with the ternary operator:

#include 
#include 

int main()
{
         


        

Answer 1

The ternary operator is a red herring.

    printf("%zu\n", sizeof(true));

prints 4 (or whatever sizeof(int) is on your platform).

The following assumes that bool is a synonym for char or a similar type of size 1, and int is larger than char.

The reason why sizeof(true) != sizeof(bool) and sizeof(true) == sizeof(int) is simply because true is not an expression of type bool. It's an expression of type int. It is #defined as 1 in stdbool.h.

There are no rvalues of type bool in C at all. Every such rvalue is immediately promoted to int, even when used as an argument to sizeof. Edit: this paragraph is not true, arguments to sizeof don't get promoted to int. This doesn't affect any of the conclusions though.