C Language Lectures from Scratch Part 6: Structure

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提示：以下是本篇文章正文内容,下面案例可供参考

一、结构体类型的声明

1.1结构的基础知识

结构是一些值的集合,这些值称为成员变量.结构的每个成员可以是不同类型的变量

We have now learnedchar、int、short、float等等类型,But these types are isolated.
If you want to describe a complex object,Say you describe a book,Books have a price、书名、作者、出版号…

To be able to describe complex objects,There is a structure.
And because complex objects have different properties,So there are different member variables,Different member variables may have different types

1.2结构的声明

struct tag
{
    
 member-list;//成员列表
}variable-list;//变量列表,可以有,可以没有

例如描述一本书

struct Book
{
    
	char name[20];
	char author[15];
	float price;
};//There is a semicolon here,别忘记了

1.3结构成员的类型

结构的成员可以是标量、数组、指针,甚至是其他结构体.

二、结构体变量的定义及初始化

2.1The definition of the variables of the structure

#include<stdio.h>
struct Book
{
    
	char name[20];
	char author[15];
	float price;
}b1,b2;//Can be created directly behind the struct(一个或多个)变量
//这里的b1,b2是全局变量,在静态区
int main()
{
    
    //struct Book 看做一个类型
	struct Book b3;//也可以在mainCreate variables in the function
	//这里的b3是局部变量,在栈区
	return 0;
}

If you think it's too hard to write every time “struct 结构体名” to create variables hassle,可以使用typedefto rename the type

typedef struct Student
{
    
	char name[20];
	int age;
	char id[20];
}Stu;//把类型struct Student重命名为Stu
//StuYou can no longer follow variables（After the rename, no variable list is allowed）

int main()
{
    
	struct Student s1;
	Stu s2;//s1和s2是一个类型
	return 0;
}

2.2Initialization of variables of a structure

struct Student
{
    
	char name[20];
	int age;
	char id[20];
};
int main()
{
    
	struct Student s1 = {
    "张三",20,"2016486001"};
	struct Student s2 = {
    "李四",19,"2016486002"};
	return 0;
}

It is possible to encounter nested definitions,Then our initialization also needs to be nested

struct M
{
    
	int a;
	char b;
};

struct N
{
    
	struct M m;
	float c;
};
int main()
{
    
	struct N t = {
     {
    1,'x'},3.14 };
	return 0;
}

Declarations do not take up space,Definitions take up space.
Statements are like drawings for building a house,The definition is to build the house according to the drawings.

三、结构体成员的访问

结构体变量访问成员 结构变量的成员是通过点操作符（.）访问的.
点操作符接受两个操作数.例如：

struct M
{
    
	int a;
	char b;
};


struct N
{
    
	struct M m;
	float c;
};
int main()
{
    
	struct N t = {
     {
    1,'x'},3.14 };
	printf("%d\n", t.m.a);//The dot can be used again“.”to access the members of the inner structure
	printf("%c\n", t.m.b);
	printf("%f\n", t.c);
	return 0;
}

但有时,What we get is not the structure itself,but the address of the structure.
这时,What if we want to access struct members？

struct M
{
    
	int a;
	char b;
};


struct N
{
    
	struct M m;
	float c;
};
int main()
{
    
	struct N t = {
     {
    1,'x'},3.14 };

	//printf("%d\n", t.m.a);//You can also use the dot again“.”to access the members of the inner structure
	//printf("%c\n", t.m.b);
	//printf("%f\n", t.c);

	struct N* pt = &t;//获取结构体t的地址
	//法一
	printf("%d %c %f\n",(*pt).m.a, (*pt).m.b, (*pt).c);
	//*pt,对pt进行解引用,就得到了t,（*pt）.m就相当于t.m

	//法二
	printf("%d %c %f\n", (pt->m).a, (pt->m).b,pt->c);
	//pt是指向结构体t的指针,m是结构体t的成员变量
	//We prescribe a way of writingpt->m就相当于t.m
	return 0;
}

四、结构体传参

请看下面代码：

struct S
{
    
	int data[1000];
	int num;
};
struct S s = {
     {
    1,2,3,4}, 1000 };
//结构体传参
void print1(struct S s)
{
    
	printf("%d\n", s.num);
}
//结构体地址传参
void print2(struct S* ps)
{
    
	printf("%d\n", ps->num);
}
int main()
{
    
	print1(s);  //传结构体
	print2(&s); //传地址
	return 0;
}

上面的 print1 和 print2 函数哪个好些？
答案是：首选print2函数. 原因：

函数传参的时候,参数是需要压栈的. 如果传递一个结构体对象的时候,结构体过大,参数压栈
的的系统开销比较大,所以会导致性能的下降.

But if the parameter you pass is just an address,也就是4个字节（64位下8字节）啊,This is much more performance friendly