C vs C++ sizeof [duplicate]

Question

I just came across this simple code snippet and am wondering why output of this program when it's compiled by a C compiler is 4 and when it's compiled by a C++ one is 8.

#include <stdio.h>  int x;  int main(){     struct x {int a; int b;};     printf("%d", sizeof(x));     return 0; } 

C++ output is rational (8 = 4 + 4 = sizeof(x.a) + sizeof(x.b)), but output of C isn't. So, how does sizeof work in C?

• C : https://ideone.com/zj5Qd2
• C++ : https://ideone.com/ZZ4v6S

Seems C prefers global variables over local ones. Is it right?

Answer 1

In C, a struct definition like struct x { int a; int b; }; does not define a type x, it defines a type struct x. So if you remove the int x; global, you'll find the C version does not compile.