拷貝建構函式和賦值函數

//拷貝建構函式呼叫的三種情況
//1.用一個類去初始化另一個類 A a; A b(a);
//2.類物件作爲函數參數傳遞，void fun(A a);
//3.函數的返回值爲類物件 A fun(){A a;return a;}

#include <stdio.h>
#include <string.h>
#include <iostream>
using namespace std;

char* mystrcpy(char *dest,const char*src){
	if (src == NULL)
	{
		return NULL;
	}
	if (dest == NULL)
	{
		return NULL;
	}
	char *p = dest;
	while (*src != '\0')
	{
		 *p = *src;
		 p++;
		 src++;
		 if (*p == '\0')
		 {
			 break;
		 }
	}
	*p = '\0';

	return dest;
}
class A
{
	void*   m_pData;
	int 	m_nSize;

public:
	A(){
	   m_pData = NULL;
	   m_nSize = 0;
	}
	A(int sz){
		if (sz > 0)
		{
			m_nSize = sz;
			m_pData = (void*)(new char[m_nSize]);
		}
	}
	//拷貝建構函式呼叫的三種情況
	//1.用一個類去初始化另一個類 A a; A b(a);
	//2.類物件作爲函數參數傳遞，void fun(A a);
	//3.函數的返回值爲類物件  A fun(){A a;return a;}
	A(const A &a){
		cout<<"拷貝建構函式呼叫\n";
		m_nSize = a.m_nSize;
		if(m_nSize>0){
			m_pData = (void*)(new char[m_nSize]);
		}
	}
	A& operator =(const A &a){
		cout<<"賦值呼叫\n";
		A a1;
		a1.m_nSize = a.m_nSize;
		if(a1.m_nSize>0){
			a1.m_pData = (void*)(new char[m_nSize]);
		}
		return a1;
	}
};

//2
void fun(A a){

}

//3
A func(){
	A a;
	return a; 
}

int main(){
	A a;
	A b(a);//1

	fun(a);
	A c = func();

	//賦值運算
	c = b;


	while(1);
	return 0;
}

輸出：
拷貝建構函式呼叫
拷貝建構函式呼叫
拷貝建構函式呼叫
賦值呼叫