学步园

 一直对C++中的try catch结构非常的疑惑。

编写了如下代码来查看被throw的对象，怎样被catch到的。

// test.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <cstdlib>
#include <new>
#include <iostream>  
#include <string>  

using namespace std;  


class object
{
 static int i;
 int locali;
public:
 ~object()
 {
  cout<<"~object()"<<locali<<endl;
 }
 object():locali(0)
 {
  i++;
  locali=i;
  cout<<"object(): "<<locali<<endl;

 }

 friend ostream& operator<<(ostream& io,object obj)
 {
  return io<<"object: "<<obj.locali;
 }
protected:
private:
};

int object::i=0;

int f()
{
 throw object();
 cout<<"throwed"<<endl;
 return 1;
}

int main() { 
 try{
  f();
  cout<<"end f()"<<endl;
 }
 catch(object& obj)
 {
  cout<<obj<<endl;
 }
 getchar();
}   

该程序的结果为：

object(): 1
~object()1
object: 1~object()1

~object()1

很是奇怪啊。

析构函数被调用了三次，构造函数只调用了一次。

并且cout<<obj<<endl;中的endl换行没有打出来。

下面这段继承的throw对象程序，输出也有问题：

// test.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <cstdlib>
#include <new>
#include <iostream>  
#include <string>  

using namespace std;  


class object
{
protected:
	string str;
	static int i;
	int locali;
public:
	virtual ~object()
	{
		cout<<"~object()"<<locali<<endl;
	}
	object():locali(0),str("object")
	{
		i++;
		locali=i;
		cout<<"object(): "<<locali<<endl;

	}

	friend ostream& operator<<(ostream& io,object obj)
	{
		return io<<obj.str<<": "<<obj.locali;
	}
protected:
private:
};

class derived: public object
{
public:
	derived():object()
	{
		str="derived";
		i++;
		locali=i;
		cout<<"derived(): "<<locali<<endl;
	}

	virtual ~derived()
	{
		cout<<"~derived()"<<locali<<endl;
	}
};

int object::i=0;

int f()
{
	throw derived();
	cout<<"throwed"<<endl;
	return 1;
}

int main() { 
	try{
		f();
		cout<<"end f()"<<endl;
	}
	catch(object& obj)
	{
		cout<<obj
			<<endl;
	}
	getchar();
}   

输出为：

object(): 1
derived(): 2
derived: 2~object()2

~derived()2
~object()2

~object()被多执行了一次。非常的奇怪。