C语言高级（四）结构体

结构体

1.1结构体基础知识

1.1.1结构体类型的定义

struct Person{
	char name[64];
	int age;
};

typedef struct _PERSON{
	char name[64];
	int age;
}Person;

注意：定义结构体类型时不要直接给成员赋值，结构体只是一个类型，编译器还没有为其分配空间，只有根据其类型定义变量时，才分配空间，有空间后才能赋值。

1.1.2 结构体变量的定义

struct Person{
	char name[64];
	int age;
}p1; //定义类型同时定义变量


struct{
	char name[64];
	int age;
}p2; //定义类型同时定义变量


struct Person p3; //通过类型直接定义

1.1.3 结构体变量的初始化

struct Person{
	char name[64];
	int age;
}p1 = {"john",10}; //定义类型同时初始化变量

struct{
	char name[64];
	int age;
}p2 = {"Obama",30}; //定义类型同时初始化变量

struct Person p3 = {"Edward",33}; //通过类型直接定义

1.1.4 结构体成员的使用

struct Person{
	char name[64];
	int age;
};
void test(){
	//在栈上分配空间
	struct Person p1;
	strcpy(p1.name, "John");
	p1.age = 30;
	//如果是普通变量，通过点运算符操作结构体成员
	printf("Name:%s Age:%d\n", p1.name, p1.age);

	//在堆上分配空间
	struct Person* p2 = (struct Person*)malloc(sizeof(struct Person));
	strcpy(p2->name, "Obama");
	p2->age = 33;
	//如果是指针变量，通过->操作结构体成员
	printf("Name:%s Age:%d\n", p2->name, p2->age);
}

1.1.5 结构体赋值

1）赋值基本概念

   相同的两个结构体变量可以相互赋值，把一个结构体变量的值拷贝给另一个结构体，这两个变量还是两个独立的变量。

struct Person{
	char name[64];
	int age;
};

void test(){
	//在栈上分配空间
	struct Person p1 = { "John" , 30};
	struct Person p2 = { "Obama", 33 };
	printf("Name:%s Age:%d\n", p1.name, p1.age);
	printf("Name:%s Age:%d\n", p2.name, p2.age);
	//将p2的值赋值给p1
	p1 = p2;
	printf("Name:%s Age:%d\n", p1.name, p1.age);
	printf("Name:%s Age:%d\n", p2.name, p2.age);
}

2）深拷贝和浅拷贝

//一个老师有N个学生
typedef struct _TEACHER{
	char* name;
}Teacher;


void test(){
	
	Teacher t1;
	t1.name = malloc(64);
	strcpy(t1.name , "John");

	Teacher t2;
	t2 = t1;

	//对手动开辟的内存，需要手动拷贝
	t2.name = malloc(64);
	strcpy(t2.name, t1.name);

	if (t1.name != NULL){
		free(t1.name);
		t1.name = NULL;
	}
	if (t2.name != NULL){
		free(t2.name);
		t1.name = NULL;
	}
}

1.1.6 结构体数组

struct Person{
	char name[64];
	int age;
};

void test(){
	//在栈上分配空间
	struct Person p1[3] = {
		{ "John", 30 },
		{ "Obama", 33 },
		{ "Edward", 25}
	};

	struct Person p2[3] = { "John", 30, "Obama", 33, "Edward", 25 };
	for (int i = 0; i < 3;i ++){
		printf("Name:%s Age:%d\n",p1[i].name,p1[i].age);
	}
	printf("-----------------\n");
	for (int i = 0; i < 3; i++){
		printf("Name:%s Age:%d\n", p2[i].name, p2[i].age);
	}
	printf("-----------------\n");
	//在堆上分配结构体数组
	struct Person* p3 = (struct Person*)malloc(sizeof(struct Person) * 3);
	for (int i = 0; i < 3;i++){
		sprintf(p3[i].name, "Name_%d", i + 1);
		p3[i].age = 20 + i;
	}
	for (int i = 0; i < 3; i++){
		printf("Name:%s Age:%d\n", p3[i].name, p3[i].age);
	}
}

1.2结构体嵌套指针

1.2.1结构体嵌套一级指针

struct Person{
	char* name;
	int age;
};

void allocate_memory(struct Person** person){
	if (person == NULL){
		return;
	}
	struct Person* temp = (struct Person*)malloc(sizeof(struct Person));
	if (temp == NULL){
		return;
	}
	//给name指针分配内存
	temp->name = (char*)malloc(sizeof(char)* 64);
	strcpy(temp->name, "John");
	temp->age = 100;

	*person = temp;
}

void print_person(struct Person* person){
	printf("Name:%s Age:%d\n",person->name,person->age);
}

void free_memory(struct Person** person){
	if (person == NULL){
		return;
	}
	struct Person* temp = *person;
	if (temp->name != NULL){
		free(temp->name);
		temp->name = NULL;
	}

	free(temp);
}

void test(){
	
	struct Person* p = NULL;
	allocate_memory(&p);
	print_person(p);
	free_memory(&p);
}

1.2.3 结构体嵌套二级指针

//一个老师有N个学生
typedef struct _TEACHER{
	char name[64];
	char** students;
}Teacher;

void create_teacher(Teacher** teacher,int n,int m){

	if (teacher == NULL){
		return;
	}

	//创建老师数组
	Teacher* teachers = (Teacher*)malloc(sizeof(Teacher)* n);
	if (teachers == NULL){
		return;
	}

	//给每一个老师分配学生
	int num = 0;
	for (int i = 0; i < n; i ++){
		sprintf(teachers[i].name, "老师_%d", i + 1);
		teachers[i].students = (char**)malloc(sizeof(char*) * m);
		for (int j = 0; j < m;j++){
			teachers[i].students[j] = malloc(64);
			sprintf(teachers[i].students[j], "学生_%d", num + 1);
			num++;
		}
	}

	*teacher = teachers;	
}

void print_teacher(Teacher* teacher,int n,int m){
	for (int i = 0; i < n; i ++){
		printf("%s:\n", teacher[i].name);
		for (int j = 0; j < m;j++){
			printf("  %s",teacher[i].students[j]);
		}
		printf("\n");
	}
}

void free_memory(Teacher** teacher,int n,int m){
	if (teacher == NULL){
		return;
	}

	Teacher* temp = *teacher;

	for (int i = 0; i < n; i ++){
		
		for (int j = 0; j < m;j ++){
			free(temp[i].students[j]);
			temp[i].students[j] = NULL;
		}

		free(temp[i].students);
		temp[i].students = NULL;
	}

	free(temp);

}

void test(){
	
	Teacher* p = NULL;
	create_teacher(&p,2,3);
	print_teacher(p, 2, 3);
	free_memory(&p,2,3);
}