给大宝贝儿写的C语言练习题

C语言练习.md

• 共用体中辨析多个字节变量如何存储在内存中？详见union.c

union.c

#include <stdio.h>

int main(){
        // 输出各种类型的长度
        printf("sizeof(short): %ld\n", sizeof(short));
        printf("sizeof(int):   %ld\n", sizeof(int));
        printf("sizeof(long):  %ld\n", sizeof(long));
        printf("sizeof(char):  %ld\n", sizeof(char));
        union{
                short i[2];
                long k;
                char c[4];
        }r, *s = &r;
        printf("sizeof(r):     %ld\n", sizeof(r));

        // 输出共用体变量内部变量的地址
        printf("i[0]@ %p\n", &r.i[0]);
        printf("i[1]@ %p\n", &r.i[1]);
        printf("k   @ %p\n", &r.k);
        printf("c[0]@ %p\n", &r.c[0]);
        printf("c[1]@ %p\n", &r.c[1]);
        printf("c[2]@ %p\n", &r.c[2]);
        printf("c[3]@ %p\n", &r.c[3]);

        // 可以看出i[0]、k、c[0]共用同一个地址
        s -> i[0] = 0x39;
        s -> i[1] = 0x38;
        printf("s->c[0]: %x\n", s -> c[0]);
        // i[0] 与 c[0] c[1] 占用相同的两个字节
        // i[1] 与 c[2] c[3] 占用相同的两个字节 
        s -> c[0] = 0x80;
        s -> c[1] = 0x81;
        s -> c[2] = 0x82;
        s -> c[3] = 0x83;
        printf("s->i[0]: %hx\n", s -> i[0]);
        // 输出 8180 
        printf("s->i[1]: %hx\n", s -> i[1]);
        // 输出 8382 
        // 说明地址高的(c[1]比c[0]地址号大)在高位，地址低的在低位

}