探索1——#pragma pack()

分别对#pragma pack(1)和#pragma pack(8)进行了测试。

测试平台：Ubuntu 15.04，32位
GCC版本：4.9.2

测试代码：

#include <stdio.h>

// #pragma pack(8)
#pragma pack(1)
typedef struct s1{
    short a;
    long b;
} S1;

typedef struct s2{
    char c;
    S1 d;
    long long e;
} S2;
#pragma pack()

int main(void)
{
    S1 s1 = {0xEEFF, 0xAABBCCDD};
    S2 s2 = {0x11, {0x2233, 0x44556677}, 0x8899EEFF};
    int s1_size = sizeof(s1);
    int s2_size = sizeof(s2);
    int i;
    unsigned char *s1_p = (unsigned char *)&s1;
    unsigned char *s2_p = (unsigned char *)&s2;

    printf("char:%d, short:%d, int:%d, long:%d, long long:%d, float:%d, double:%d\n",
        sizeof(char), sizeof(short), sizeof(int), sizeof(long), sizeof(long long), \
        sizeof(float), sizeof(double));

    printf("s1 addr: %08x, s2 addr: %08x\n", (unsigned int)s1_p, (unsigned int)s2_p);
    printf("s1 size: %d byte\n", s1_size);
    for(i = 0; i < s1_size; i++) {
        printf("%02x ", s1_p[i]);
    }
    printf("\n");

    printf("s2 size: %d byte\n", s2_size);
    for(i = 0; i < s2_size; i++) {
        printf("%02x ", s2_p[i]);
    }
    printf("\n");

    return 0;
}

#pragma pack(1)测试结果：

#pragma pack(8)测试结果：

参考：
[1] http://blog.csdn.net/lime1991/article/details/44536343
[2] http://blog.csdn.net/21aspnet/article/details/6730124