测试环境：

#include<stdio.h>
int main(){//1字节对齐struct XXX{unsigned char ch;unsigned int in;unsigned short si;}__attribute__((packed));struct XXX xxx;printf("%zd\n",sizeof(xxx));//7#pragma pack(1)struct YYY{unsigned char ch;unsigned int in;unsigned short si;};struct YYY yyy;printf("%zd\n",sizeof(yyy));#pragma pack()//不进行对齐限制，编译器决定//默认对齐方式是采用当前最长的变量的长度作为对齐方式struct ZZZ{unsigned char ch;unsigned int in;unsigned short si;};struct ZZZ zzz;printf("%zd\n",sizeof(zzz));//12return 0;
}