引用(个人学习笔记黑马学习)

1、引用的基本语法

#include <iostream>
using namespace std;

int main() {

	int a = 10;
	//创建引用
	int& b = a;

	cout << "a = " << a << endl;
	cout << "b = " << b << endl;

	b = 100;
	cout << "a = " << a << endl;
	cout << "b = " << b << endl;
	system("pause");
	return 0;
}

---

2、引用的注意事项

#include <iostream>
using namespace std;

int main() {

	int a = 10;

	//1、引用必须初始化
	//int& b; 错，必须初始化
	int& b = a;

	//2、引用在初始化后，不可以改变
	int c = 20;

	b = c;//赋值操作，而不是更改引用
	cout << "a = " << a << endl;
	cout << "b = " << b << endl;
	cout << "c = " << c << endl;



	system("pause");
	return 0;
}

---

3、引用做函数参数

#include <iostream>
using namespace std;



	//交换函数

	//1、值传递
	void mySwap01(int a, int b) {
		int temp = a;
		a = b;
		b = temp;
		/*cout << "swap01 a = " << a << endl;
		cout << "swap01 b = " << b << endl;*/
}

	//2、地址传递
	void mySwap02(int* a,int* b) {
		int temp = *a;
		*a = *b;
		*b = temp;
	}

	//3、引用传递
	void mySwap03(int &a,int &b) {
		int temp = a;
		a = b;
		b = temp;
	}

int main() {

	int a = 10;
	int b = 20;
	//mySwap01(a, b);//值传递，形参不会修饰实参

	//mySwap02(&a, &b);地址传递，形参会修饰实参

	mySwap03(a, b);//引用传递，形参会修饰实参

	cout << "a = " << a << endl;
	cout << "b = " << b << endl;


	system("pause");
	return 0;
}

---

4、引用做函数的返回值

#include <iostream>
using namespace std;

//引用做函数的返回值
//1、不要返回局部变量的引用
int& test01() {
	int a = 10;//局部变量存放在四区中的栈区
	return a;
}

//2、函数的调用可以作为左值
int& test02() {
	static int a = 10;//静态变量 存放在全局区，全局区的数据存放在程序结束后系统释放
	return a;
}


int main() {

	//int& ref = test01();

	//cout << "ref = " << ref << endl;//第一次结果正确，是因为编译器做了保留
	//cout << "ref = " << ref << endl;//第二次结果错误，是因为a的内存已经释放


	int& ref2 = test02();
	cout << "ref2 = " << ref2 << endl;
	cout << "ref2 = " << ref2 << endl;

	test02() = 1000;//如果函数的返回值是引用，这个函数调用可以作为左值

	cout << "ref2 = " << ref2 << endl;
	cout << "ref2 = " << ref2 << endl;

	system("pause");
	return 0;
}

---

5、引用的本质

引用的本质是指针常量

#include <iostream>
using namespace std;


void func(int& ref) {
	ref = 100;//red是引用，转化为*ref=100
}



int main() {

	int a = 10;

	//自动转换成 int* const ref=&a;  指针常量是指针指向不可改变，
	int& ref = a;
	ref = 20;//内部发现ref是引用，自动帮我们转换为：*ref=20;

	cout << "a：" << a << endl;
	cout << "ref：" << ref << endl;

	func(a);
	system("pause");
	return 0;
}

---

6、常量引用

#include <iostream>
using namespace std;

//打印数据函数
void showValue(const int& val) {

	//val = 1000;
	cout << "val = " << val << endl;
}


int main() {

	//常量引用
	//使用场景：用来修饰形参，防止误操作

	int a = 100;
	//int& ref = 10;引用必须引一块合肥的内存空间

	加上const之后 编译器将代码修改  int temp=10; const int& ref=temp;
	//const int& ref = 10;
	//ref = 20;//报错，加入const之后变为只读，不可以修改

	showValue(a);

	cout << "a = " << a << endl;
	system("pause");
	return 0;
}