结构体中包含二级指针案例

小咪咪 2022-05-13 14:08 182阅读 0赞

给出如下结构体，要求全部在堆区开辟空间。有多个老师，每个老师有多个学生。

typedef struct
    {
    	char *name;//老师
    	int stu_num;//学生数
    	char **stu_arr;//学生名字
    }TEACHER;

需要注意以下问题：

1.  此问题使用双层循环即可解决。
2.  外层循环处理这三个成员变量：给name开辟空间；给stu\_num赋值；给stu\_arr开辟5个连续的保存一级地址地char\*\*类型的空间。即给成员变量赋值。
3.  在内层循环中使用stu\_arr5个char\*类型的空间开辟，每个均开辟5个char\*类型的空间，再给他们赋值。当然，这个过程(内层循环)要执行25次。即给二级地址中引用的一级地址开辟空间并赋值。

#define _CRT_SECURE_NO_WARNINGS
    #include<stdio.h>
    #include<stdlib.h>
    #include<string.h>
    typedef struct
    {
    	char *name;
    	int stu_num;
    	char **stu_arr;
    }TEACHER;
    
    int main(int argc, char *argv[])
    {
    	TEACHER **teachers = (TEACHER **)calloc(5, sizeof(TEACHER));
    	for (int i = 0; i < 5; i++)
    	{
    		//*name
    		teachers[i] = (TEACHER*)calloc(1, sizeof(TEACHER));
    		teachers[i]->name = (char *)calloc(32, sizeof(char));
    		strcpy(teachers[i]->name, "lao_shi");
    		printf("%s\n", teachers[i]->name);
    		
    		//stu_num
    		teachers[i]->stu_num = 3;
    		printf("%d\n", teachers[i]->stu_num);
    		
    		//**stu_arr 
    		teachers[i]->stu_arr = (char **)calloc(5, sizeof(char *));
    		printf("%p\n", teachers[i]->stu_arr);
    		
    		for (int j = 0; j < 5; j++)
    		{
    			//*stu_arr
    			teachers[i]->stu_arr[j] = (char *)calloc(teachers[i]->stu_num, 128 * sizeof(char));
    			strcpy(teachers[i]->stu_arr[j], "xiao_ming");
    			printf("%s\n", teachers[i]->stu_arr[j]);
    		}
    	}
    
    	//释放
    	for (int i = 0; i < 5; i++)
    		for (int j = 0; j < 5; j++)
    			if (teachers[i]->stu_arr[j]) free(teachers[i]->stu_arr[j]), teachers[i]->stu_arr[j] = NULL;
    
    	for (int i = 0; i < 5; i++) if (teachers[i]) free(teachers[i]), teachers[i] = NULL;
    
    	if (teachers) free(teachers), teachers = NULL;
    	
    	
    	system("pause");
    	return 0;
    }