Question

这是我第一次处理异常，但在理解异常时遇到了一些问题。这是我的C ++作业。我需要你们的帮助。当我在此站点上向大家询问时，我总是会找到解决问题的方法。谢谢！

这是我运行程序时得到的输出：

An exception test is about to take place.

AnnounceDestroyed已创建。 AnnounceDestroyed被销毁。 -1

将要进行异常测试。 AnnounceDestroyed已创建。 AnnounceDestroyed被销毁。错误！

将要进行异常测试。 AnnounceDestroyed已创建。尝试了异常，但没有发生。 AnnounceDestroyed被销毁。没有发生异常。

我在我的两个虚函数中使用了throw，它们似乎工作正常，但是当我在第三个函数中尝试使用它时，编译器给我一个错误。如果向下滚动，则会在编译器给我错误的地方找到我的注释。这是我的代码：

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


    class AnnounceDestroyed
    {
        public:
        AnnounceDestroyed(){std::cout << "AnnounceDestroyed is created."   << std::endl;}
       ~AnnounceDestroyed(){std::cout << "AnnounceDestroyed is destroyed." << std::endl;}
    };

    class ExceptionThrower
    {
        public:
            virtual void launchException() = 0;
            virtual ~ExceptionThrower(){};
    };

    class IntThrower : public ExceptionThrower
    {
        private:
            int thrwVar;
        public:
            IntThrower(int var){thrwVar = var;}
            void launchException()
        {
            throw thrwVar;
        }
    };

    class MsgThrower : public ExceptionThrower
    {
        private:
            string msgStr;
        public:
            MsgThrower(string str){msgStr = str;}
        void launchException()
        {
            throw msgStr;
        }

    };

    class CustomThrower : public ExceptionThrower
    {
        private:
            int customInt;
            string customStr;
        public:
            CustomThrower(int cstmInt, string cstmString)
                         {customInt = cstmInt; customStr = cstmString;}
            void launchException()
        {
            //throw customStr; // when I user throw here compiler gives me an error for some reasons.
// here is the error : "Thread 1: signal SIGABRT"
            //throw customInt;   // And here as well.
        }
    };

    class CustomException
    {
        private:
            int cstmExpInt;
            string cstmExpStr;
        public:
            CustomException(int aInt, string bStr)
                          {cstmExpInt = aInt; cstmExpStr = bStr;}
        void printContents()
        {

            std::cout << cstmExpStr << std::endl;
            std::cout << cstmExpInt << std::endl;
        }
    };


    void activateException(ExceptionThrower &currentThrower)
    {
        shared_ptr<AnnounceDestroyed> announce = make_shared<AnnounceDestroyed>();
        currentThrower.launchException();
        std::cout << "An exception was attempted, but did not occur." << std::endl;
    }

    int main()
    {
        // Constants
        const int INT_THROWER_CODE = -1;
        const string MSG_THROWER_STRING = "Error!";
        const int CUSTOM_THROWER_CODE = -99;
        const string CUSTOM_THROWER_STRING = "Major error!";

        int exceptionCounter = 0;

        IntThrower LauncherInt(INT_THROWER_CODE);
        MsgThrower LauncherMsg(MSG_THROWER_STRING);
        CustomThrower LauncherCustom(CUSTOM_THROWER_CODE, CUSTOM_THROWER_STRING);

        try {
            std::cout << "An exception test is about to take place." << std::endl;
            activateException(LauncherInt);
            std::cout << "An exception did not take place." << std::endl;

        }
        catch (int &a)
        {
            std::cout << a << std::endl;
            std::cout << std::endl;


        }
        try {
            std::cout << "An exception test is about to take place." << std::endl;
            activateException(LauncherMsg);
            std::cout << "An exception did not take place." << std::endl;

        }
        catch (string &b)
        {
            std::cout << b << std::endl;
            std::cout << std::endl;

        }
        try {
            std::cout << "An exception test is about to take place." << std::endl;
            activateException(LauncherCustom);
            std::cout << "An exception did not take place." << std::endl;
            std::cout << std::endl;
        }
        catch (CustomException &c)
        {
            c.printContents();

        }    
    }

Answer 1

您需要一个“ throw”子句来引发异常。

如果将'launchException'更改为：也许会得到想要的东西

void launchException() override
    {
         std::cout << customInt << std::endl;
         std::cout << customStr << std::endl;
         throw CustomException(customInt, customStr);
    }

还要注意“ override”关键字。这可能有助于避免您在评论中提到的警告。

第一次处理异常。我很难理解异常

1 个答案: