Question

在观看在线教程并阅读之后，我很难理解异常处理。我试图通过测试驱动开发，我不能。到目前为止我想出的是这个。我应该使用这个结构

struct ArrayException
{
    ArrayException(string newMessage = "error") :message(newMessage)
    {
    }

    string message;
};

第一次尝试。

int sum(int* theArray, unsigned int arraySize)
{
    try
    {

        if (theArray = NULL)
        {
            throw ArrayException("NULL ARRAY REFERENCE");
        }
    }
    catch (int* param)
    {
        cout << "you can't have " << param << " as an array size";
    }
    int sum = 0;
    for (int i = 1; i < arraySize; i++)
    {
        sum += theArray[i];
    }
    return sum;
}

我也尝试过这样做。

int sum(int* theArray, unsigned int arraySize)
{

    if (theArray = NULL)
    {
        throw ArrayException("NULL ARRAY REFERENCE");
    }
    else
    {
        int sum = 0;
        for (int i = 1; i < arraySize; i++)
        {
            sum += theArray[i];
        }
        return sum;
    }
}

Answer 1

虽然这篇文章没有特别提及，但我认为问题是为什么没有抓住异常？答案很简单 - 因为抛出的异常是ArrayException类型，而catch是使用int *类型完成的。

Answer 2

掌握这些东西的最佳方法是推荐πάνταῥε：获得一本好书。这是开始选择书籍的好地方：The Definitive C++ Book Guide and List

其余的是带有注释的代码块，我认为它们是必需的。

#include <iostream>
// removed the using namespace std;
struct ArrayException
{
    ArrayException(std::string newMessage = "error") :
            message(newMessage)
    {
    }

    std::string message;
};

int sum(int* theArray, size_t arraySize) // change made here:
    // size_t better suited than unsigned int for indexes
{
    //throw std::out_of_range("BOOM!"); //uncomment to trigger a std::exception
    //throw 42; // uncomment to trigger the unknown exception

    if (theArray == NULL)
    {
        throw ArrayException("NULL ARRAY REFERENCE"); //perfect!
    }
    else
    {
        int sum = 0;
        for (size_t i = 0; i < arraySize; i++) // changes made here: 
            // size_t not int to get rid of signed/unsigned conflict
            // starting with array index 0, not 1
        {
            sum += theArray[i];
        }
        return sum;
    }
}

int main()
{
    try
    {
        sum (NULL, 10); // NULL address to force the exception
    }
    catch (ArrayException & param) // catch the custom exception
        // catch by reference where possible
    {
        std::cout << "This bad stuff happened: " << param.message << std::endl;
    }
    // extra stuff to show what can also be done
    catch (std::exception & stdexcpt) // catch any standard exceptions and 
                                  // print their message
    {
         std::cout << "Standard exception thrown: " << stdexcpt.what() << std::endl;
    }
    catch (...) // catch anything else that was thrown and doesn't 
                // correspond to any expectation 
    {
         std::cout << "No idea what happened." << std::endl;
    }
}

很难理解异常处理c ++

2 个答案: