#pragma pack

#include <stdio.h>

#pragma pack(1)
struct A {
    char a;
    int b;
};

#pragma pack(2)
struct B {
    char a;
    int b;
};

#pragma pack(4)
struct C {
    char a;
    int b;
};

int main(void) {
    printf("sizeof A = %zu\n", sizeof(struct A));
    printf("sizeof B = %zu\n", sizeof(struct B));
    printf("sizeof C = %zu\n", sizeof(struct C));
    return 0;
}

C

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