test_3_18

test_3_18

#define _crt_secure_no_warnings 1

#include <stdio.h>


struct s
{
	char c1;//1
	int i;//4
	char c2;//1
};

struct s2
{
	char c1;
	char c2;
	int i;
};


struct s3
{
	double d;//8 8 8
	char c;  //1 8 1
	int i;   //4 8 4
};

struct s4
{
	char c1;
	struct s3 s3;
	double d;
};

int main()
{
	//struct s s = { 0 };
	//struct s2 s2 = { 0 };
	//struct s3 s3 = { 0 };
	struct s4 s4 = { 0 };
	printf("%zd\n", sizeof(s4));//size_t

	return 0;
}

#pragma pack(1)
struct s
{
    char c1;//1 1 1
    int i;  //4 1 1
    char c2;//1 1 1
};
#pragma pack()


int main()
{
    printf("%zd\n", sizeof(struct s));

    return 0;
}



struct s
{
	int arr[1000];
	int n;
	double d;
};

void print1(struct s tmp)
{
	int i = 0;
	for (i = 0; i < 5; i++)
	{
		printf("%d ", tmp.arr[i]);
	}
	printf("%d ", tmp.n);
	printf("%lf\n", tmp.d);
}

void print2(const struct s* ps)
{
	int i = 0;
	for (i = 0; i < 5; i++)
	{
		printf("%d ", ps->arr[i]);
	}
	printf("%d ", ps->n);
	printf("%lf ", ps->d);
}

int main()
{
	struct s s = { {1,2,3,4,5}, 100, 3.14 };
	//print1(s);
	print2(&s);

	return 0;
}


位段式的结构
struct s
{
	int _a:2;
	int _b:5;
	int _c:10;
	int _d:30;
};


int main()
{
	printf("%zd\n", sizeof(struct s));

	return 0;
}



struct s
{
    char a : 3;
    char b : 4;
    char c : 5;
    char d : 4;
};

int main()
{
    struct s s = { 0 };
    s.a = 10;
    s.b = 12;
    s.c = 3;
    s.d = 4;
    printf("%zd\n", sizeof(s));
    return 0;
}




struct a
{
    int _a : 2;
    int _b : 5;
    int _c : 10;
    int _d : 30;
};


int main()
{
    struct a sa = { 0 };
    //scanf("%d", &(sa._b));//这是错误的

    //正确的示范
    int b = 0;
    scanf("%d", &b);
    sa._b = b;

    return 0;
}

union un
{
	char c;//1
	int i; //4
};


int main()
{
	union un u = {0};
	printf("%zd\n", sizeof(u));//4

	printf("%p\n", &u);
	printf("%p\n", &(u.i));
	printf("%p\n", &(u.c));

	return 0;
}

union un
{
	char c;//1
	int i; //4
};


int main()
{
	union un u = { 0 };
	u.i = 0x11223344;
	u.c = 0x55;

	return 0;
}



union un
{
	char c[5];//5
	int i; //4
};


int main()
{
	union un u = { 0 };
	printf("%zd\n", sizeof(u));
	return 0;
}



union un
{
	short s[7];//14  2 8 2
	int i; //4 8 4
};

int main()
{
	union un u = { 0 };
	printf("%zd\n", sizeof(u));
	return 0;
}



struct gift_list
{
    int stock_number;//库存量
    double price; //定价
    int item_type;//商品类型

    union {
        struct 
        {
            char title[20];//书名
            char author[20];//作者
            int num_pages;//页数
        }book;
        struct 
        {
            char design[30];//设计
        }mug;
        struct 
        {
            char design[30];//设计
            int colors;//颜色
            int sizes;//尺寸
        }shirt;
    }item;
};

int main()
{
    struct gift_list gl;
    
    return 0;
}


写一个程序，判断当前机器是大端？还是小端？

int check_sys()
{
	int n = 1;
	return *(char*)&n;
}


int check_sys()
{
	union un
	{
		char c;
		int i;
	}u;
	u.i = 1;
	return u.c;//小端：返回1，大端：返回0
}

int main()
{
	int ret = check_sys();//小端：返回1，大端：返回0
	if (ret == 1)
		printf("小端\n");
	else
		printf("大端\n");
	return 0;
}