异常 堆栈解退

//函数出现异常而终止，程序将释放堆栈重内存，并一直向上释放，只到找到一个try块中的返回地址

//重新引发异常   将捕获的异常继续传回上一个try块

///////////////////////////////////////////////
//
//exc_mean.h
//
///////////////////////////////////////////////
#include<iostream>

class bad_hmean
{
private:
 double v1;
 double v2;
public:
 bad_hmean(double a=0,double b=0):v1(a),v2(b){}
 void mesg();
};

inline void bad_hmean::mesg()
{
 std::cout<<"hmean("<<v1<<", "<<v2<<"):"
  <<"invaild arguments:a=-b\n";
}

class bad_gmean
{
public:
 double v1;
 double v2;
 bad_gmean(double a=0,double b=0):v1(a),v2(b){}
 const char * mesg();
};

inline const char * bad_gmean::mesg()
{
 return "gmean() arguments should be >=0\n";
}

 

///////////////////////////////////////////////////////
//
//error.cpp
//
///////////////////////////////////////////////////////
//error5.cpp -- unwinding the stack
#include <iostream>
#include <cmath> //for  sqrt()
#include <cstring>
#include "exc_mean.h"

class demo
{
private:
 char word[40];
public:
 demo (const char * str)
 {

  std::strcpy(word, str);
  std::cout << "demo " << word << " created\n";
 }
 ~demo()
 {
  std::cout << "demo " << word << " destroyed\n";
 }
 void show() const
 {
  std::cout << "demo " << word << " lives!\n";
 }
};

// function prototypes
double hmean(double a, double b) throw(bad_hmean);
double gmean(double a, double b) throw(bad_gmean);
double means(double a, double b) throw(bad_hmean, bad_gmean);

int main()
{
 using std::cout;
 using std::cin;
 using std::endl;

 double x, y, z;
 demo d1("found in main()");
 cout << "Enter two numbers: ";
 while (cin >> x >> y)
 {
  try {                  // start of try block
   z = means(x,y);
   cout << "The mean mean of " << x << " and " << y
    << " is " << z << endl;
   cout << "Enter next pair: ";
  }// end of try block
  catch (bad_hmean & bg)    // start of catch block
  {
   bg.mesg();
   cout << "Try again.\n";
   continue;
  }                 
  catch (bad_gmean & hg)
  {
   cout << hg.mesg();
   cout << "Values used: " << hg.v1 << ", "
    << hg.v2 << endl;
   cout << "Sorry, you don't get to play any more.\n";
   break;
  } // end of catch block
 }
 d1.show();
 cout << "Bye!\n";
 return 0;
}

double hmean(double a, double b) throw(bad_hmean)
{
 if (a == -b)
  throw bad_hmean(a,b);
 return 2.0 * a * b / (a + b);
}

double gmean(double a, double b) throw(bad_gmean)
{
 if (a < 0 || b < 0)
  throw bad_gmean(a,b);
 return std::sqrt(a * b);
}

double means(double a, double b) throw(bad_hmean, bad_gmean)
{
 double am, hm, gm;
 demo d2("found in means()");
 am = (a + b) / 2.0;    // arithmetic mean
 try
 {
  hm = hmean(a,b);
  gm = gmean(a,b);
 }
 catch (bad_hmean & bg) // start of catch block
 {
  bg.mesg();
  std::cout << "Caught in means()\n";
  throw;             // 重新引发异常传回main()找try       
 }         
 d2.show();
 return (am + hm + gm) / 3.0;
}