程序基石系列之拷贝构造

当需要用同类的对象来创建一个新的对象的时候，那个类的拷贝构造函数就会被调用来构造这个对象。

#include <iostream>
using namespace std;

static int objectCount =0;

class HowMany{
public:
	HowMany(){objectCount++;print("HowMany()");}
	HowMany(int i){	objectCount++;print("HowMany(int)");}
	void print(const string& msg =""){
		if(msg.size()!=0) cout <<msg<<":";
		cout<<"ObjectCount = "<<objectCount<<endl;
	}

	~HowMany(){	objectCount--;print("~HowMany()");
	}
};

//Pass and return BY VALUE
HowMany f(HowMany x) {
	cout<<"begin of f";
	x.print("x argument insides f()");
	cout<<"end of f()"<<endl;
	return 0;
}

int main(int arg, char* avg[]){
	HowMany h;
	h.print("after construction of h");
	HowMany h2 =h;
	h.print("after call to h");
	//f(h);
	//h.print("after call to f()");
	return 0;
}

输出结果：

HowMany():ObjectCount = 1
after construction of h:ObjectCount = 1
after call to h:ObjectCount = 1
~HowMany():ObjectCount = 0
~HowMany():ObjectCount = -1

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