重載構造函數、缺省參數構造函數及析構函數

學習C++過程中，把學習到的點滴做些記錄吧

碰到兩個功能實現很相近的構造函數：重載和缺省。雖然功能實現差不多，但還是有些區別：

//重載函數的功能實現

class complex
{
private:
	double real;
	double imag;
public:
	//構造函數
	complex(double r,double i)
	{
		real=r;
		imag=i;
	}
	//構成重載函數
	complex()
	{
		real=2.0;
		imag=2.0;
	}
	complex(double m)
	{
		real=4.0;
		imag=m;
	}
	//析構函數
	~complex()
	{
		cout<<"the space has released!\n";
	}
	//得到複數的實部和虛部
    double realcomplex()
	{
		return real;
	}
	double imagcomplex()
	{
		return imag;
	}
	//計算模
	double abscomplex()
	{
		double t;
		t=real*real+imag*imag;
		return sqrt(t);
	}
};  

void main()
{
	complex a(1.12,2.13);
	complex b;
	complex c(2.45);
	
	cout<<"real of a:"<<a.realcomplex()<<"\n"<<"imag of a:"<<a.imagcomplex()<<"\n"
		<<"abs of a:"<<a.abscomplex()<<endl;
	cout<<"real of b:"<<b.realcomplex()<<"\n"<<"imag of b:"<<b.imagcomplex()<<"\n"
		<<"abs of b:"<<b.abscomplex()<<endl;
	cout<<"real of c:"<<c.realcomplex()<<"\n"<<"imag of c:"<<c.imagcomplex()<<"\n"
		<<"abs of c:"<<c.abscomplex()<<endl;
	system("pause");
}  

//缺省參數構造函數功能實現

#include "stdafx.h"
#include <iostream>
#include <math.h>
using namespace std;

class complex
{
private:
	double real;
	double imag;
public:
	//構造函數
	complex(double r=1.0,double i=1.0)
	{
		real=r;
		imag=i;
	}
	//析構函數
	~complex()
	{
		cout<<"the space has released!\n";
	}
	//得到複數的實部和虛部
    double realcomplex()
	{
		return real;
	}
	double imagcomplex()
	{
		return imag;
	}
	//計算模
	double abscomplex()
	{
		double t;
		t=real*real+imag*imag;
		return sqrt(t);
	}
};  //再次強調定義類時要“；”

void main()
{
	complex a(1.12,2.13);
	complex b;
	complex c(2.45);
	
	cout<<"real of a:"<<a.realcomplex()<<"\n"<<"imag of a:"<<a.imagcomplex()<<"\n"
		<<"abs of a:"<<a.abscomplex()<<endl;
	cout<<"real of b:"<<b.realcomplex()<<"\n"<<"imag of b:"<<b.imagcomplex()<<"\n"
		<<"abs of b:"<<b.abscomplex()<<endl;
	cout<<"real of c:"<<c.realcomplex()<<"\n"<<"imag of c:"<<c.imagcomplex()<<"\n"
		<<"abs of c:"<<c.abscomplex()<<endl;
	system("pause");
}  

可以看出，重載函數在調用時要嚴格匹配到參數個數，且在函數定義時不能給定初值。而缺省參數函數在調用時比較靈活，既可以給定初值，還不用限定參數個數。當時想這樣的話爲什麼還有重載去實現呢？呵呵，只是這種應用場景罷了，重載在其他場合大有用處。

再記錄下析構函數，析構主要是在最後釋放對象的分配空間。析構和構造是對應的，在調用時有多少個對象系統就默認產生多少個析構函數，且運行析構的順序和構造函數定義的順序相反,析構函數是不存在重載的概念。