demo_exception_handling_1.cpp

对于一个初涉VC＋＋的人来书

//****************************************************
// 三角形条件的异常检测
//****************************************************

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

# include <iostream>
# include <cmath>
using namespace std;

double triangle(double,double,double);

int main()
{
	cout<<"begin of main()"<<endl;
	cout<<endl;

	double a,b,c,area;

	cout<<"input three sides of triganle: ";
	cin>>a>>b>>c;

	//try块进行异常检测:检测以下语句中的函数调用是否产生异常
	//引发异常后跳出try语句体,控制转向catch语句
	//try块之后必须是花括号复合语句,即使只有一个语句
	try
	{
		while(a>0 && b>0 && c>0)
		{
			area=triangle(a,b,c);
			cout<<"area of triangle is: "<<area<<endl;
			cout<<endl;
			cout<<"input three sides of triganle: ";
			cin>>a>>b>>c;
		}
	}

	//不允许在try块和catch之间插入任何其它语句
//	cout<<"Throw exception and await process ..."<<endl; 

	//被检测到的异常被catch捕获并作相应处理
	//try块之后必须是花括号复合语句,即使只有一个语句
	catch(double)
	{
		cout<<"a="<<a<<",b="<<b<<",c="<<c<<": that is not a traingle!"<<endl;
	}
	
	cout<<endl;
	cout<<"end of main()"<<endl;
	
	return 0;
}
  
double triangle(double a,double b,double c)
{
	cout<<"begin of triangle()"<<endl;

	double s=(a+b+c)/2,area;
	
	//当引发一个异常时,抛出异常信息
	//同时,不再执行函数随后语句,控制返回到调用程序
//	if(a+b<=c||b+c<=a||c+a<=b) throw a;    //异常类型为double
	if(a+b<=c||b+c<=a||c+a<=b) throw 1.0;  //OK! double类型

	//注意: 类型匹配过程不作任何类型转换,下面都是错误的情况:
	//若找不到类型匹配catch异常处理块:编译连接没问题,但执行错误,
	//提示: abnormal program termination
//	if(a+b<=c||b+c<=a||c+a<=b) throw 1.0f; //异常类型为float
//	if(a+b<=c||b+c<=a||c+a<=b) throw 1;    //异常类型为int   
//	if(a+b<=c||b+c<=a||c+a<=b) throw 1L;   //异常类型为long int 	
	
	area=sqrt(s*(s-a)*(s-b)*(s-c));

	cout<<"end of triangle()"<<endl;

	return area;
}

/*
begin of main()

input three sides of triganle: 3 4 5
begin of triangle()
end of triangle()
area of triangle is: 6

input three sides of triganle: 1 2 1
begin of triangle()
a=1,b=2,c=1: that is not a traingle!

end of main()
*/