Question

请参见以下代码的预期流程

在这种情况下，基类异常由于其多态性而被捕获为这种预期行为。

#include <stdio.h>
#include<iostream.h>
using namespace std;
void main() {

    try {
        //throw CustomException();
        throw bad_alloc();
    }
    ///due to poly morphism base class reference will
    catch(exception &ex) {
        cout<<"Base :"<<ex.what()<<endl;
    }

    catch(bad_alloc &ex) {
        cout<<"Derieved :"<<ex.what()<<endl;
    }
}

输出

 bad_alloc

但是，如果我要像下面的代码中所示进行自定义异常，则即使基类捕获首先出现在catch块中，派生类也将捕获该异常：

class CustomException : exception {

public :
     CustomException() { }

     const char * what() const throw() {
         // throw new exception();
         return "Derived Class Exception !";
     }
};

void main() {
    try {
        throw CustomException();
        //throw bad_alloc();
    }
    ///due to poly morphism base class reffrence will
    catch(exception &ex) {
        cout<<"Base :"<<ex.what()<<endl;
    }

    catch(CustomException &ex) {
        cout<<"Derived :"<<ex.what()<<endl;
    }
}

预期输出：

Base : Derived Class Exception !

实际输出：

Derived: Derived Class Exception !

Answer 1

使用class关键字声明的类的默认继承访问说明符是private。这意味着CustomException继承自exception private ly。使用private继承的派生类不能绑定到对其父类的引用。

如果您继承public，它将可以正常工作：

class CustomException : public exception // <-- add public keyword here
{
public :
     CustomException()
     {
     }

     const char * what()
     {
         return "Derived Class Exception !";
     }
};

int main()
{

    try
    {
        throw CustomException();
    }
    catch(exception &ex)
    {
        cout<<"Base :"<<ex.what()<<endl;
    }

    catch(CustomException &ex)
    {
        cout<<"Derived :"<<ex.what()<<endl;
    }
}

Live Demo

基类捕获不捕获异常，即使该异常出现在派生类捕获之前

1 个答案: