帮忙看看c++异常捕获try{}catch{}throw为什么throw不能返回一个具体对象

[木兮₀₃₂₁]

请诸位看一下为什么会这样！
exc_mean.hpp

#include<iostream>
using namespace std;
class bad_hmean
{
    private:
        double v1;
        double v2;
    public:
        bad_hmean(int a=0,int b=0):v1(a),v2(b){}
        void mesg();

};
inline void bad_hmean::mesg()
{
    cout<<"heman("<< v1 <<" , "<<v2<<"): "
    <<"invalid 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 () srguments should be >0 \n";
}

error4.cpp

#include<iostream>
#include<cmath>
#include"exc_mean.hpp"
using namespace std;
double hmean(double a,double b);
double gmean(double a,double b);

int main()
{
    double x,y,z;
    cout<<"Enter two numbers: ";
    while(cin>>x>>y)
    {
        try
        {
            z=hmean(x,y);
            cout<<"Harmonic mean of "<<x<<" and "<<y<<" is "<<z<<endl;
            cout<<"Geometric mean of "<<x<<" and "<<y<<" is "<<gmean(x,y)<<endl;
            cout<<"enter next set of numbers <q to quit> : ";
        }
        catch(bad_hmean &bh)
        {
            bh.mesg();
            cout<<"Try again! \n";
            continue;
        }
        catch(bad_gmean &bg)
        {
            cout<<bg.mesg();
            cout<<"Values uesd "<<bg.v1<<" , "<<bg.v2<<endl;
            cout<<"Sorry ,you don't play again. \n";
            break;
        }
    }
    cout<<"Bye! \n";
    return 0;
}

double hmean(double a,double b)
{
    if(a==-b)
    //原句如下，编译运行没问题   
   //将此句替换成右边的两句，编译错误                 // bad_hmean A=bad_hmean(a,b);
    throw bad_hmean(a,b);                                     //throw A;
    return 2.0*a*b/(a+b);
}
double gmean(double a, double b)
{
    if(a<0||b<0)
throw bad_gmean(a,b);
   /* bad_gmean B=bad_gmean(a,b);//
    throw B;*/
    return sqrt(a*b);
}

报错如下：
error4.cpp:50:11: error: use of undeclared identifier 'A'
throw A;
^
error4.cpp:57:11: error: use of undeclared identifier 'B'
throw B;
^
2 errors generated.

怎么还说使用未声明的标示符 A和B
我不是已经创建了A B这两个对象了吗？
到底怎么回事？
求解

[kongl123]

哪个编译器这么蛋疼?

[木兮₀₃₂₁]

引用 1 楼 kongl123 的回复:

哪个编译器这么蛋疼?

gdb

[kongl123]

不是吧,什么版本?我试了gcc没有这问题啊.规范定义的应该是throw expression;没有问题

[木兮₀₃₂₁]

引用 4楼lm_whales 的回复:

if(a==-b)
        bad_hmean A=bad_hmean(a,b);
        throw A;

这种代码不报错才是怪事 起码加上大括号吧

if(a==-b){
        bad_hmean A=bad_hmean(a,b);
        throw A;
}

受教了，粗心了

[paschen]

if 后如果不加括号，只对后一条语句有效，这样你的定义是在if里，但throw不是在if里，故找不到，加上大括号就好了

[lm_whales]

if(a==-b)
        bad_hmean A=bad_hmean(a,b);
        throw A;

这种代码不报错才是怪事 起码加上大括号吧

if(a==-b){
        bad_hmean A=bad_hmean(a,b);
        throw A;
}