c語言——結構體嵌套二級指針

c語言——結構體嵌套二級指針

如果一個結構體內嵌套二級指針了二級指針，這裏的students爲二級指針，也對應了一對多的關係，一個老師，多個學生。

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

我們知道，二級指針指向一級指針的地址，三級指針指向二級指針的地址

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

	int ret = 0;
	ret = allocateSpace(&teachers);
	if (ret < 0)
	{
		printf("allocateSpace 函數調用出錯!\n");
		return;
	}

	//打印老師及其學生信息
	printTeachers(teachers);

	//釋放內存
	freeSpace(teachers);
	teachers = NULL;

}

分配空間

int allocateSpace(struct Teacher ***temp)
{
	if (NULL == temp)
	{
		//錯誤碼 不同錯誤碼錶示不同錯誤
		return -1;
	}

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

		//給老師結構體指針分配空間
		ts[i] = malloc(sizeof(struct Teacher));

		//給老師名字分配空間
		ts[i]->name = malloc(sizeof(char) * 64);
		sprintf(ts[i]->name, "Teacher_%d", i + 1);

		//給學生指針分配內存
		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;
}

打印與釋放

打印

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]);
		}
	}
}

釋放

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;
}

運行

Teacher_1
   Teacher_1_Stu_1
   Teacher_1_Stu_2
   Teacher_1_Stu_3
   Teacher_1_Stu_4
Teacher_2
   Teacher_2_Stu_1
   Teacher_2_Stu_2
   Teacher_2_Stu_3
   Teacher_2_Stu_4
Teacher_3
   Teacher_3_Stu_1
   Teacher_3_Stu_2
   Teacher_3_Stu_3
   Teacher_3_Stu_4