C语言之——__attribute__

#include <stdio.h>

struct mystruct11 
{
    int a;
    char b;
    short c;
}__attribute__((packed));

struct mystruct21 
{
    char a;
    int b;
    short c;
}__attribute__((packed));

struct p  
{  
    int a;  
    char b;  
    char c;  
}__attribute__((aligned(4))) p1;



struct q  
{  
    int a;  
    char b;  
    struct p qn;  
    char c;  
}__attribute__((aligned(8))) q2;

int main(void)
{
    printf("sizeof(struct mystruct11) = %d.\n",sizeof(struct mystruct11));
    printf("sizeof(struct mystruct21) = %d.\n",sizeof(struct mystruct21));
    /*
    两个不同结构体1字节对齐的结构
    struct mystruct11                         struct mystruct21
    1字节对齐                          1字节对齐
    4                                                   1
    1                                                   4
    2                                                   2
    */
    
    printf("sizeof(int):%d, sizeof(char)=%d\n", sizeof(int), sizeof(char));
    printf("sizeof(p1):%d\n", sizeof(p1));

    printf("sizeof(q2):%d\n", sizeof(q2));
    
    return 0;
}

sizeof(struct mystruct11) = 8.
sizeof(struct mystruct21) = 10.
sizeof(int):4, sizeof(char)=1
sizeof(p1):8
sizeof(q2):24

--------------------------------
Process exited after 0.01857 seconds with return value 0
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