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记得看书上说值传递时异常会被构造三次，引用传递会被构造两次，指针传递才会只构造一次，今天试了一个，却只有值传递只被构造两次，其它两种方式只构造一次，在Cygwin和VC++ 9.0上都试了，结果一样，测试代码如下：

#include
#include

using std::cout;
using std::string;

class MyException
{
public:
    MyException(const string& name, int no)
        : m_name(name), m_no(no)
    {
        cout<    }

    MyException(const MyException& old)
        :m_name(old.m_name), m_no(old.m_no)
    {
        cout<    }

    ~MyException( void )
    {
        cout<    }
    string m_name;
    int m_no;

};

int main(int argc, char* argv[])
{
    try{
        throw MyException("value exception",1 );
    }
    catch(MyException ex)
    {
        cout<<"caught exception:"<    }

    try{
        throw MyException("reference exception", 2);
    }
    catch(MyException& ex)
    {
        cout<<"caught exception:"<    }

    try{
        MyException* pe = new MyException("pointer exception", 3);
        throw pe;
    }
    catch(MyException* pe){
        cout<<"caught exception:"<m_name<        delete pe;
    }
}

测试结果：

1:value exception : MyException::MyException( )
1:value exception is copied
caught exception:value exception
1 :MyException::~MyException( )
1 :MyException::~MyException( )
2:reference exception : MyException::MyException( )
caught exception:reference exception
2 :MyException::~MyException( )
3:pointer exception : MyException::MyException( )
caught exception:pointer exception
3 :MyException::~MyException( )

还需要再证实一下。