【c++】用构造函数实现初始化的方法

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2022 年 06 月 28 日

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## 一：空参构造函数

```cpp
#include<iostream>
using namespace std;

class Time{
	private:
		int hour;
		int minute;
		int sec;
	public:
		// 空参 构造函数 
		Time(){
			hour = 0;
			minute = 0;
			sec = 0;
		}

public:
		friend ostream & operator << (ostream & output, Time & t);
};

ostream & operator << (ostream & output, Time & t){
	output << "时: " << t.hour << " 分：" << t.minute << " 秒：" << t.sec << endl; 
}

int main(){

Time t1 = Time();
	cout << t1;
	return 0;
} 
```

## 二：带参数的构造函数

```cpp
#include<iostream>
using namespace std;

class Time{
	private:
		int hour;
		int minute;
		int sec;
	public:
		// 带参数构造函数 
		Time(int h, int m, int s){
			hour = h;
			minute = m;
			sec = s;
		}

public:
		friend ostream & operator << (ostream & output, Time & t);
};

ostream & operator << (ostream & output, Time & t){
	output << "时: " << t.hour << " 分：" << t.minute << " 秒：" << t.sec << endl; 
}

int main(){

Time t1 = Time(1, 2, 3);
	cout << t1;
	return 0;
} 
```

## 三：在构造函数中使用参数初始化表

```cpp
#include<iostream>
using namespace std;

class Time{
	private:
		int hour;
		int minute;
		int sec;
	public:
		// 参数初始化表构造函数 
		Time(int h, int m, int s) : hour(h), minute(m), sec(s){
		};

public:
		friend ostream & operator << (ostream & output, Time & t);
};

ostream & operator << (ostream & output, Time & t){
	output << "时: " << t.hour << " 分：" << t.minute << " 秒：" << t.sec << endl; 
}

int main(){

Time t1 = Time(1, 2, 3);
	cout << t1;
	return 0;
} 
```

## 四：使用默认参数构造函数

```cpp
#include<iostream>
using namespace std;

class Time{
	private:
		int hour;
		int minute;
		int sec;
	public:
		// 默认参数构造函数 
		Time(int h = 0, int m = 0, int s = 0){
			hour = h;
			minute = m;
			sec = s;
		}

public:
		friend ostream & operator << (ostream & output, Time & t);
};

ostream & operator << (ostream & output, Time & t){
	output << "时: " << t.hour << " 分：" << t.minute << " 秒：" << t.sec << endl; 
}

int main(){

Time t1 = Time();
	cout << t1;
	return 0;
} 
```

## 五：构造函数重载

```cpp
#include<iostream>
using namespace std;

class Time{
	private:
		int hour;
		int minute;
		int sec;
	public:
		// 空参 构造函数 
		Time(){
			hour = 0;
			minute = 0;
			sec = 0;
		}

// 参数初始化表 构造函数 
		Time(int h, int m, int s) : hour(h), minute(m), sec(s) {};

public:
		friend ostream & operator << (ostream & output, Time & t);
};

ostream & operator << (ostream & output, Time & t){
	output << "时: " << t.hour << " 分：" << t.minute << " 秒：" << t.sec << endl; 
}

int main(){

Time t1 = Time(1, 2, 3);
	Time t2 = Time();
	cout << t1 << t2 << endl;
	return 0;
} 
```