【C++】C++异常

try
{
    //保护的标识代码
}
catch(ExceptionName e1)
{
    //catch块
}
catch(ExceptionName e2)
{
    //catch块
}
catch(ExceptionName eN)
{
    //catch块
}

double Division(int a, int b)
{
  // 当b == 0时抛出异常
  if (b == 0)
    throw "Division by zero condition!";
  else
    return ((double)a / (double)b);
}
void Func()
{
  // 这里可以看到如果发生除0错误抛出异常，另外下面的array没有得到释放。
  // 所以这里需要捕获所有类型的异常，然后先将array释放，然后再将捕获的异常重新抛出，交给外面处理
  int* arr = new int[10];
  try
  {
    int len, time;
    cin >> len >> time;
    cout << Division(len, time) << endl;
  }
  catch (...)
  {
    cout << "delete []" << arr << endl;
    delete[] arr;
    throw;
  }
  //...
  cout << "delete []" << arr << endl;
  delete[] arr;
}
void Test2()
{
  try
  {
    Func();
  }
  catch (const char* errmsg)
  {
    cout << errmsg << endl;
  }
  catch (...)
  {
    cout << "unkown exception" << endl;
  }
}

int at(vector<int>& v, size_t pos) noexcept
{
  if (pos >= v.size())
    throw out_of_range("数组越界");
  else
    return v[pos];
}
void Test1()
{
  vector<int> v = {1, 2, 3, 4, 5};
  try {
    at(v, 5);
  }
  catch (out_of_range& errmsg)
  {
    cout << errmsg.what() << endl;
  }
  catch (...) {
    cout << "未知异常" << endl;
  }
}

void Test2()
{
  vector<int> v(10);
  try {
    v.reserve(100000000);
    v.at(20) = 5;
  }
  catch (exception& errmsg)
  {
    cout << errmsg.what() << endl;
  }
  catch (...)
  {
    cout << "unknow Exception" << endl;
  }
}

class Exception//这里定义了一个异常的基类，后面对于不同类型的异常，将进行不同的继承
{
public:
    Exception(const string& errmsg, int id)
        :_errmsg(errmsg)
        ,_id(id)
    {}
    virtual string what() const//这里的what使用virtual修饰，以达到多态使用，返回不同的错误信息
    {
        return _errmsg;
    }
protected:
    string _errmsg;
    int _id;
};
class SqlException : public Exception//sql类型的异常
{
public:
    SqlException(const string& errmsg, int id, const string& sql)
        :Exception(errmsg, id)
        , _sql(sql)
    {}
    virtual string what() const//对虚函数进行重写，实现多态
    {
        //修改异常信息并返回
        string str = "SqlException:";
        str += _errmsg;
        str += "->";
        str += _sql;
        return str;
    }
private:
    const string _sql;//保存出现错误的sql语句
};
class CacheException : public Exception//Cache类型异常
{
public:
    CacheException(const string& errmsg, int id)
        :Exception(errmsg, id)
    {}
    virtual string what() const//虚函数重写
    {
        string str = "CacheException:";
        str += _errmsg;
        return str;
    }
};
class HttpServerException : public Exception//网络类型异常
{
public:
    HttpServerException(const string& errmsg, int id, const string& type)
        :Exception(errmsg, id)
        , _type(type)
    {}
    virtual string what() const
    {
        string str = "HttpServerException:";
        str += _type;
        str += ":";
        str += _errmsg;
        return str;
    }
private:
    const string _type;
};
void SQLMgr()
{
    srand(time(nullptr));
    if (rand() % 4 == 0)
    {
        throw SqlException("权限不足", 100, "select * from name = '张三'");
    }
    //throw "xxxxxx";
}
void CacheMgr()
{
    srand(time(0));
    if (rand() % 5 == 0)
    {
        throw CacheException("权限不足", 100);
    }
    else if (rand() % 6 == 0)
    {
        throw CacheException("数据不存在", 101);
    }
    SQLMgr();//如果没有抛出异常就调用SQL层操作
}
void HttpServer()
{
    // ...
    srand(time(0));
    if (rand() % 3 == 0)
    {
        throw HttpServerException("请求资源不存在", 100, "get");
    }
    else if (rand() % 4 == 0)
    {
        throw HttpServerException("权限不足", 101, "post");
    }
    CacheMgr();//如果网络服务没有问题，在这里调用内存操作
}
void Test3()
{
    while(1)
    {
        this_thread::sleep_for(chrono::seconds(1));
        try{
            HttpServer();//这里调用网络服务
        }
        catch (const Exception& e) // 这里捕获父类对象就可以
        {
            // 多态
            cout << e.what() << endl;
        }
        catch (...)
        {
            cout << "Unkown Exception" << endl;
        }
    }
}