19.结构体深入

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本文详细介绍了C语言中结构体的拷贝机制，包括基本类型和指针类型的拷贝，以及如何正确处理结构体内的指针以避免内存泄漏和重复释放。通过实例展示了结构体嵌套指针的内存分配、打印和释放过程。

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结构体拷贝：

1.结构体中的变量都是栈分配的存储空间，可以直接使用“=”拷贝

void test01()
{
	
	struct Person person1 = { "aaa", 20 };
	struct Person person2 = { "bbb", 30 };
 
	//赋值操作
	person1 = person2;
 
	printf("Name:%s Age:%d\n",person1.name,person1.age);
	printf("Name:%s Age:%d\n",person2.name,person2.age);
}

2.如果是结构体中有成员变量是指针，需要注意先释放需要被填充的结构体变量中的指针变量，再拷贝。因为这种拷贝会导致2个问题，结构体变量的指针变量teacher2.name被释放2次，同时也会导致teacher1内存泄漏

if (teacher1.name != NULL)
	{
		free(teacher1.name);
		teacher1.name = NULL;
	}
 
	teacher1.name = malloc(strlen(teacher2.name) + 1);
	strcpy(teacher1.name, teacher2.name);
	teacher1.age = teacher2.age;

结构体拷贝

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
 
struct Person
{
	char name[64];
	int age;
};
 
void test01()
{
	
	struct Person person1 = { "aaa", 20 };
	struct Person person2 = { "bbb", 30 };
 
	//赋值操作
	person1 = person2;
 
	printf("Name:%s Age:%d\n",person1.name,person1.age);
	printf("Name:%s Age:%d\n",person2.name,person2.age);
}
 
 
struct Teacher
{
	char *name;
	int age;
};
 
void test02()
{
	struct Teacher teacher1;
	teacher1.name = malloc(sizeof(char)* 64);
	memset(teacher1.name, 0, 64);
	strcpy(teacher1.name, "aaa");
	teacher1.age = 20;
 
	struct Teacher teacher2;
	teacher2.name = malloc(sizeof(char)* 128);
	memset(teacher2.name, 0, 128);
	strcpy(teacher2.name, "bbbbbbbbbbbbb");
	teacher2.age = 30;
 
	printf("Name:%s Age:%d\n", teacher1.name,teacher1.age);
	printf("Name:%s Age:%d\n", teacher2.name, teacher2.age);
 
 
	printf("teacher1 size: %d\n",sizeof(teacher1));
	printf("teacher2 size: %d\n", sizeof(teacher2));
 
	//赋值操作
	//不使用默认的结构体赋值行为
	//teacher1 = teacher2;
	//如果结构体内部有指针指向堆内存，那么就不能使用编译器默认的赋值行为，应该手动控制赋值过程。
 
	//----------------------------------------------
 
	if (teacher1.name != NULL)
	{
		free(teacher1.name);
		teacher1.name = NULL;
	}
 
	teacher1.name = malloc(strlen(teacher2.name) + 1);
	strcpy(teacher1.name, teacher2.name);
	teacher1.age = teacher2.age;
 
	//----------------------------------------------
 
 
	printf("---------------\n");
	printf("Name:%s Age:%d\n", teacher1.name, teacher1.age);
	printf("Name:%s Age:%d\n", teacher2.name, teacher2.age);
 
	//释放堆内存
	if (teacher1.name != NULL)
	{
		free(teacher1.name);
		teacher1.name = NULL;
	}
 
	if (teacher2.name != NULL)
	{
		free(teacher2.name);
		teacher2.name = NULL;
	}
 
}
 
 
int main(){
 
	//test01();
	test02();
 
	system("pause");
	return EXIT_SUCCESS;
}

结构体嵌套一级指针

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string.h>
#include<stdlib.h>

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

//分配内存
struct Person** allocateSpace()
{
	struct Person **temp = malloc(sizeof(struct Person *) * 3);

	for (int i = 0; i < 3; ++i)
	{
		temp[i] = malloc(sizeof(struct Person));

		temp[i]->name = malloc(sizeof(char)* 64);

		sprintf(temp[i]->name, "Name_%d", i + 1);

		temp[i]->age = 100 + i;
	}


	return temp;
}

//打印
void printPerson(struct Person **person)
{
	if (NULL == person)
	{
		return;
	}

	for (int i = 0; i < 3; ++i)
	{
		printf("Name:%s Age:%d\n",person[i]->name,person[i]->age);
	}
}

//释放内存
void freeSpace(struct Person **person)
{

	if (NULL == person)
	{
		return;
	}

	for (int i = 0; i < 3; ++i)
	{
		if (person[i] == NULL)
		{
			continue;
		}

		if (person[i]->name != NULL)
		{
			printf("Name:%s的内存被释放!\n", person[i]->name);
			free(person[i]->name);
			person[i]->name = NULL;
		}

		
		free(person[i]);
		person[i] = NULL;
	}

	free(person);
	person = NULL;
}

void test()
{
	struct Person **person = NULL;
	person = allocateSpace();
	printPerson(person);
	freeSpace(person);
	person = NULL;
}

int main(){

	test();

	system("pause");
	return EXIT_SUCCESS;
}

结构体嵌套二级指针

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string.h>
#include<stdlib.h>

struct Teacher
{
	char *name;
	char **students;
};

int allocateSpace(struct Teacher ***temp)
{
	if (NULL == temp)
	{
		//错误码 不同错误码表示不同错误
		return -1;
	}

	struct Teacher **ts = malloc(sizeof(struct Teacher *) * 3);
	for (int i = 0; i < 3; ++i)
	{

		//给老师结构体指针分配空间
		ts[i] = malloc(sizeof(struct Teacher));

		//给老师名字分配空间
		ts[i]->name = malloc(sizeof(char) * 64);
		sprintf(ts[i]->name, "Teacher_%d", i + 1);

		//给学生指针分配内存
		ts[i]->students = malloc(sizeof(char *)* 4);
		for (int j = 0; j < 4; ++j)
		{
			ts[i]->students[j] = malloc(sizeof(char) * 64);
			sprintf(ts[i]->students[j],"%s_Stu_%d",ts[i]->name,j + 1);

		}

	}

	*temp = ts;

	return 0;
}

void printTeachers(struct Teacher **teachers)
{
	if (NULL == teachers)
	{
		return;
	}

	for (int i = 0; i < 3; ++i)
	{
		printf("%s\n", teachers[i]->name);
		for (int j = 0; j < 4; ++j)
		{
			printf("   %s\n",teachers[i]->students[j]);
		}
	}
}


void freeSpace(struct Teacher **teachers)
{
	if (NULL == teachers)
	{
		return; 
	}

	for (int i = 0; i < 3; ++i)
	{

		if (teachers[i] == NULL)
		{
			continue;
		}

		if (teachers[i]->name != NULL)
		{
			free(teachers[i]->name);
			teachers[i]->name = NULL;
		}

		for (int j = 0; j < 4; ++j)
		{
			if (teachers[i]->students[j] != NULL)
			{
				free(teachers[i]->students[j]);
				teachers[i]->students[j] = NULL;
			}
		}

		free(teachers[i]->students);
		teachers[i]->students = NULL;


		free(teachers[i]);
		teachers[i] = NULL;
	}

	free(teachers);
	teachers = NULL;
}

void test()
{
	
	struct Teacher **teachers = NULL;

	int ret = 0;
	ret = allocateSpace(&teachers);
	if (ret < 0)
	{
		printf("allocateSpace 函数调用出错!\n");
		return;
	}

	//打印老师及其学生信息
	printTeachers(teachers);

	//释放内存
	freeSpace(teachers);
	teachers = NULL;

}


int main(){

	test();

	system("pause");
	return EXIT_SUCCESS;
}