alignchar.c

#include <stdio.h>

main()
{
struct A {
   int a;
   char b;
   short c;
   };

struct B {
    char b;
    int a;
    short c;
    };

#pragma pack(2) /*指定按2字节对齐*/
struct C {
    char b;
    int a;
    short c;
    };
#pragma pack() /*取消指定对齐，恢复缺省对齐*/

#pragma pack(1)  /*指定按1字节对齐 */
struct D {
   char b;
   int a;
   short c;
   };
#pragma pack() /*取消指定对齐，恢复缺省对齐 */

int s1=sizeof(struct A);
int s2=sizeof(struct B);
int s3=sizeof(struct C);
int s4=sizeof(struct D);

printf("%d\n",s1);
printf("%d\n",s2);
printf("%d\n",s3);
printf("%d\n",s4);
}

output.txt

8

12

8

7