C语言 __attribute__ ((packed)) 使用

Question

C语言使用__attribute__ ((packed))
测试的struct 占用字节大小感到挺奇怪, 不能理解 (详细见图)

软件: Dev 5.6.3
编译: TDM-GCC 4.8.1 32

源代码:

#include <stdio.h>

typedef struct 
{
    char A; //1
    int B; //4
    char C; //1
    double D; //8
    char E; //1

}__attribute__ ((packed)) StructA;

struct StructB
{
    char A;
    int B;
    char C;
    double D;
    char E;
}; 

int main(void)
{

    StructA StructAExample;
    struct StructB StructBExample;
    
    printf("short 占用的字节 %d \n", sizeof(short));
    printf("int 占用的字节 %d \n", sizeof(int));
    printf("double 占用的字节 %d \n", sizeof(double));
    printf("StructA 占用的字节 %d \n", sizeof(StructAExample));
    printf("StructB 占用的字节 %d \n", sizeof(StructBExample));

    return 0;
}

Answer 1

https://blog.csdn.net/yihui8/article/details/109752425