异常机制

异常机制

try块(可能异常的代码块)　　catch块(捕获异常)　　throw块(引发异常)

//////////////////////////////////////
//
//error.cpp
//
///////////////////////////////////////
#include <iostream>
double hmean(double a,double b);

int main(void)
{
 using namespace std;
 double x,y,z;

 cout<<"enter two number: ";
 while (cin>>x>>y)
 {
  try                             //try
  {
   z=hmean(x,y);
  }
  catch (const char * s)         //catch 
  {
   cout<<s<<endl;
   cout<<"enter a new pair of numbers: ";
   continue;
  }
  cout<<"mean of "<<x<<" and "<<y<<" is "<<z<<endl;
  cout<<"enter next set of numbers <q to quit>: ";
 }
 cout<<"bye!\n";
 return 0;
}

double hmean(double a,double b)
{
 if (a==-b)
  throw "bad hmean() arguments: a=-b not allowed";    //throw
 return 2.0*a*b/(a+b);
 
}