[C++知识库]C语言———关于结构体（结构体对齐规则）

一、结构体的定义

1.1

struct date
{
	char c[20];
    double weight;
    double length;
    int age;
};               //这里的“；”切忌不可省略

#include<stdio.h>
int main()
{
    struct date a ={"编程人",98.3,180.3,23};
    printf("%s %lf %lf %d\n",a.c,a.weight,a.length,a.age);
    return 0;
}

1.2 结构体的嵌套

struct T
{
    double weight;
    double length;
};


struct S
{
    char c;
    struct T y;
    int a;
    double d;
    char arr[100];
};


#include<stdio.h>
int main()
{
    struct S s = { 'c' ,{55.6,200} , 100 , 3.14 , "编程人" };
    printf( "%c %lf %lf %d %lf %s\n", s.c , s.y.weight,s.y.length , s.a , s.d , s.arr );
    
    return 0;
}

二、结构体的对齐规则

struct S1
{
	char c1;
	char c2;
	int a;
};

struct S2
{
	char c1;
	int a;
	char c2;
};


#include<stdio.h>
int main()
{
	struct S1 s1 = {0};
	printf("%d\n",sizeof(s1));

	struct S2 s2 = {0};
	printf("%d\n",sizeof(s2));

}

这个是我关于上面一些代码的讲解（讲的不是很好）：https://share.weiyun.com/qLSChsM8

三、求结构体各个变量的偏移量

利用offsetof函数求，头文件是stddef.h，最好还是能看一下上面的视频~~

#include<stddef.h>
#include<stdio.h>
struct s2
{
	char c;
	int i;
	double d;
};

#include<stdio.h>
int main()
{
	printf("%d\n",offsetof(struct s2,i));  //0
	printf("%d\n",offsetof(struct s2,c));  //4
	printf("%d\n",offsetof(struct s2,d));  //8
	printf("%d\n",sizeof(s2));
	return 0;
}
*/