联合体union

占用大小按字节数最大的变量来，下面的联合体的大小为4字节

typedef union MyUnion {
    char c; //1byte
    int i; //4byte
} _MyUnion;

 

int main() {
    _MyUnion v;
    printf("%x, %x\n", v.c, v.i); //未初始化时的值
    printf("%p, %p, %p\n", &v, &v.c, &v.i); //地址都一样

    v.i = 1024; //0x400
    v.c = '1'; //0x31, 只修改第1个字节, 2,3,4字节维持不变
    printf("%x, %c, %x\n", v.c, v.c, v.i);

    //遍历union的每个字节
    v.i = 0xabc;
    char *p = &v;
    char bytes = sizeof(_MyUnion);
    unsigned char ch;
    for (int i = 0; i < bytes; ++i) {
        ch = *(p + i);
        printf("%p-%x, ", p+i, ch);
    }
    printf("\n");
}