一.构造函数（C++）

内容参考于《21天学通C++》(第八版)
不去纠结C++的原理和细节，从C的角度去学习C++，再通过C++项目去加深理解

一.构造函数

1. 示例1：构造函数是可以重载

#include <iostream>
#include <string>
using namespace std;
class Human
{
private:
	string name;
	int age;

public:
	Human() // default constructor
	{
		age = 0; // initialized to ensure no junk value
		cout << "Default constructor: name and age not set" << endl;
	}

	Human(string humansName, int humansAge) // overloaded
	{
		name = humansName;
		age = humansAge;
		cout << "Overloaded constructor creates ";
		cout << name << " of " << age << " years" << endl;
	}
};

int main()
{
	Human firstMan; // use default constructor
	Human firstWoman("Eve", 20); // use overloaded constructor
}

运行结果

Default constructor: name and age not set
Overloaded constructor creates Eve of 20 years

2. 示例2：实例对象强制输入参数

直接去掉上面代码的Human()部分

	Human() // default constructor
	{
		age = 0; // initialized to ensure no junk value
		cout << "Default constructor: name and age not set" << endl;
	}

那么编译就会报错

Human firstMan;没有合适的默认构造函数可用

3. 示例3：带默认值的构造函数参数

class Human
{
private:
	string name;
	int age;
public:
	// overloaded constructor (no default constructor)
	Human(string humansName, int humansAge = 25)
	{
		name = humansName;
		age = humansAge;
		cout << "Overloaded constructor creates " << name;
		cout << " of age " << age << endl;
	}
	// ... other members
};

// 可以这样调用
Human adam("Adam"); // adam.age is assigned a default value 25
Human eve("Eve", 18); // eve.age is assigned 18 as specified

4. 示例4：包含初始化列表的构造函数

#include <iostream>
#include <string>
using namespace std;
class Human
{
private:
	int age;
	string name;

public:
	Human(string humansName = "Adam", int humansAge = 25)
		: name(humansName), age(humansAge)
	{
		cout << "Constructed a human called " << name;
		cout << ", " << age << " years old" << endl;
	}
};

int main()
{
	Human adam;
	Human eve("Eve", 18);

	return 0;
}

运行结果

Constructed a human called Adam, 25 years old
Constructed a human called Eve, 18 years old

下面语句快捷得把输入得参数设置进了成员里面

: name(humansName), age(humansAge)