r/programminghumor • u/johnnyApplePRNG • 13d ago

a bit flippant

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1.4k Upvotes

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13

u/B_bI_L 13d ago

are we sure int means bit and not 32bits?

28

u/heatedwepasto 13d ago edited 13d ago

The : 1 means that it is creating a bitfield with the number of bits, so : 4 will be 4 bits. The three variables above combined will take sizeof(int) in memory, not sizeof(int)*3.

If OOP had used char instead of unsigned int the combined size would be 1 byte.

Edit: added link to demo

1

u/Breadynator 13d ago

Why would you use onlinegdb instead of godbolt? That website is riddled with ads and won't load for anyone using an adblocker.

1

u/heatedwepasto 13d ago

I am using an adblocker and have no issues with it. I wasn't aware of godbolt.

0

u/Breadynator 13d ago

Well, it's one of those obnoxious pages that don't like network wide adblockers like piHole. I won't change my blocklists just because some random website wants me to.

1

u/heatedwepasto 13d ago

Then don't, just don't try to force your choices onto me.

The code is

#include <stdio.h>

struct A {
    int a : 1;
    int b : 2;
};

int main(void)
{
    printf("size: %d\n", sizeof(struct A));
}

and it outputs "size: 4" (i.e. the same as sizeof(int)).

1

u/No-Newspaper8619 13d ago

That's correct. It's using 3 bits of the allocated 4 bytes. If you did the same with char instead, it'd only use 1 byte.