The structure of knowledge in the corners of the C language

目录

结构体

基本语法

Define a new structure

实例化结构体

访问成员变量

Direct component selection 双目操作符 " . "

普通访问

指针访问

Indirect component selection 双目操作符 " -> "

结构体初始化

The structure is initialized uniformly

直接初始化

结构体数组的初始化

实例操作

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结构体

基本语法

Define a new structure

A structure is a data type defined by our programmers

struct 结构体名
{
    类型1 成员变量名1
    类型2 成员变量名2
    ...
};

实例化结构体

struct 结构体名 a;  //ais the new typestruct An instance of the struct name

I don't know if everyone is familiar with the instantiation of the structure ,其实“struct 结构体名”与“int”是一个意思,只不过“struct 结构体名”is our own type,而“int”是CIt is already defined in the language library,使用方法都一样,就如同我们使用“int”一样,定义一个4字节32bit的整形数,And we use our own defined structure is,定义一个“struct 结构体名”的变量.

---

访问成员变量

如上述,After we instantiate the struct,You can access member variables through some operators.For example, how should the member variables in the following structure be accessed

struct date
{
	int y;
	int m;
	int d;
};

struct student
{
	char name[32];
	int num;
	float score;
	struct date birthday;
};

---

Direct component selection 双目操作符 " . "

普通访问

组合类型变量.成员变量  ==》To get the member variable inside the composite type variable

Let's now access the member variables of the above structure after instantiation

struct student s;

s.name;
s.num;
s.score;
s.birthday;
s.birthday.y;
s.birthday.m;
s.birthday.d;

怎么样,This is still very simple,其中要注意的是,in an externally accessed struct,There are also structures,We need to first access the struct in the current struct,Then access the specific member variables.as we visit struct date 中的 y ,我们先访问struct student中的struct date birthday,再访问 struct date 中的 y,代码实现就是 s.birthday.y.

成功访问后,We can perform assignments and other operations on member variables.

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指针访问

(*结构体指针).成员变量
        *结构体指针 ==》The structure variable pointed to
            结构体变量.成员变量

有了上面的例子,这个就很简单啦

struct student *p = malloc(sizeof(struct student));

(*p).name;
(*p).num;
(*p).score;
(*p).birthday;
(*p).birthday.y;
(*p).birthday.m;
(*p).birthday.d;

Indirect component selection 双目操作符 " -> "

用法：结构体指针->成员变量名

It is still the structure we defined above,我们要如何访问呢

struct student *p = malloc(sizeof(struct student));

p->name;
p->num;
p->score;
p->birthday;
p->birthday.y;
p->birthday.m;
p->birthday.d;

值得注意的是,In this case again,访问birthdaymember variables in ,因为没有对date进行操作,Still use direct component selection,So coding is implemented as：p->birthday.m;.

---

综上,There are three ways to access member variables of a structure,According to this example,则是

struct student s;
s.成员变量;

struct student *p = malloc(sizeof(struct student));
(*p).成员变量;

struct student *p = malloc(sizeof(struct student));
p->成员变量;

---

结构体初始化

The structure is initialized uniformly

It is how the instances defined later have an initial value,Let's stick to the example above

struct date
{
	int y = 2000;
	int m = 1;
	int d = 1;
};

struct student
{
	char name[32] = 张三;
	int num = 20000101;
	float score = 0;
	struct date birthday;
};

在定义结构体时,You can assign values ​​to the member variables in the structure.This way each instantiated object will have these initial values ​​after that.

直接初始化

If we are not creating the structure,就初始化,Or like changing the initialized value,We can directly initialize the structure instance assignment.

in the order in which they were defined,依次初始化各成员变量,用逗号分开：

struct student s ={
    "张三",
    20000101,
    0,
    {
        2000,1,1
    },
}

当然,We can also define without order,Then we need to add the member variable name：

struct student s = {
    .num = 20000101,
    .name = "张三",
    .birthday = {
        2000,1,1
    },
    .score = 0
}

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结构体数组的初始化

按顺序初始化

struct student class[3] = 
{
    //class[0]
	{
		.name = "张三",
        .num = 20000101,
		.score = 0,
		.birthday = {2001,01,01}
							
	},
	//class[1]
	{
		.name = "李四",
        .num = 20000102,
		.score = 0,
		.birthday = {2001,01,02}
	},
	//class[2]
	{
		.name = "王五",
        .num = 20000103,
		.score = 0,
		.birthday = {2001,01,03}
	}			
};

同样的,We can also initialize out of order ,Medical array subscript to achieve,不过这种方式,不同编译器下,Circumstances or restrictions are different

struct student class[3] = 
{
	[1] = {
		.name = "张三",
        .num = 20000101,
		.score = 0,
		.birthday = {2001,01,01}
							
	},

	[0] = {
		.name = "李四",
        .num = 20000102,
		.score = 0,
		.birthday = {2001,01,02}
	},

	[2] = {
		.name = "王五",
        .num = 20000103,
		.score = 0,
		.birthday = {2001,01,03}
	}			
};

实例操作

有了以上的知识储备,Let's practice our hands

First define a structure to describe the situation of a student（姓名、学号、成绩,出生年、月、日）,Then define an array of structures to describe the students in our class（3个）,And enter each student's information from the keyboard,and output to the terminal.

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代码实现

#include<stdio.h>

struct date
{
	int y;
	int m;
	int d;
};

struct student
{
	char name[32];
	int num;
	float score;
	struct date birthday;
};

int main()
{
	struct student CS[3];

	for(int i = 0;i < sizeof(CS) / sizeof(struct student);i++)
	{
		scanf("%d%d%d%s%d%f",&CS[i].birthday.y,&CS[i].birthday.m,&CS[i].birthday.d,CS[i].name,&CS[i].num,&CS[i].score);
	}
	for(int i = 0;i < sizeof(CS) / sizeof(struct student);i++)
	{
		printf("%d  %d\t%d\t%s\t%d\t%f\n",CS[i].birthday.y,CS[i].birthday.m,CS[i].birthday.d,CS[i].name,CS[i].num,CS[i].score);
	}

	return 0;
}