如何优雅处理C++程序错误？——异常机制从原理到应用

#include<iostream>
using namespace std;
double Divide(int a, int b)
{
	//当b==0时抛出异常
	if (b == 0)
	{
		string s("Divide by zero andition!");
		throw s;
	}
	else
	{
		return (double)a / (b);
	}
}
void Func()
{
	int len, time;
	cin >> len >> time;
	Divide(len, time);
}
int main()
{
	Func();
	return 0;
}

#include<iostream>
using namespace std;
double Divide(int a, int b)
{
	//当b==0时抛出异常
	if (b == 0)
	{
		throw exception("Divide by zero andition!");
	}
	else
	{
		return (double)a / (b);
	}
}
void Func()
{
	int len, time;
	cin >> len >> time;
	Divide(len, time);
}
int main()
{
	try
	{
		Func();
	}
	catch (const exception& e)
	{
		cout << e.what() << endl;
        //e.what()就是说你的异常是什么
	}
	return 0;
}

double Divide(int a, int b)
{
	try
	{
		// 当b == 0时抛出异常
		if (b == 0)
		{
			string s("Divide by zero condition!");
			throw s;
		} 
		else
		{
		return ((double)a / (double)b);
		}
	} 
	catch(int errid)
		{
			cout << errid << endl;
		} 
		return 0;
} 
void Func()
{
	int len, time;
	cin >> len >> time;
	try
	{
		cout << Divide(len, time) << endl;
	} 
	catch(const char* errmsg)
	{
		cout << errmsg << endl;
	} 
	cout << __FUNCTION__ << ":" << __LINE__ << "⾏执⾏" << endl;
} 
int main()
{
	while (1)
	{
		try
		{
			Func();
		} 
		catch(const string & errmsg)
		{
			cout << errmsg << endl;
		}
	} 
	return 0;
}

#include<iostream>
using namespace std;
double Divide(int a, int b)
{
	//当b==0时抛出异常
	if (b == 0)
	{
		/*string s("Divide by zero andition!");
		throw s;*/
		throw exception("Divide by zero andition!");
	}
	else
	{
		return (double)a / (b);
	}
}
void Func()
{
	int len, time;
	cin >> len >> time;
	Divide(len, time);
}
int main()
{
	try
	{
		Func();
	}
	catch (...)
	{
		cout << "未知类型错误" << endl;
	}
	return 0;
}

#include<thread>

// 一般大型项目程序才会使用异常，下面我们模拟设计一个服务的几个模块
// 每个模块的继承都是Exception的派生类，每个模块可以添加自己的数据
// 最后捕获时，我们捕获基类就可以
class Exception
{
public:
	Exception(const string& errmsg, int id)
		:_errmsg(errmsg)
		, _id(id)
	{}

	virtual string what() const
	{
		return _errmsg;
	}

	int getid() const
	{
		return _id;
	}
protected:
	string _errmsg;
	int _id;
};

class SqlException : public Exception
{
public:
	SqlException(const string& errmsg, int id, const string& sql)
		:Exception(errmsg, id)
		, _sql(sql)
	{}

	virtual string what() const
	{
		string str = "SqlException:";
		str += _errmsg;
		str += "->";
		str += _sql;
		return str;
	}
private:
	const string _sql;
};

class CacheException : public Exception
{
public:
	CacheException(const string& errmsg, int id)
		:Exception(errmsg, id)
	{}

	virtual string what() const
	{
		string str = "CacheException:";
		str += _errmsg;
		return str;
	}
};

class HttpException : public Exception
{
public:
	HttpException(const string& errmsg, int id, const string& type)
		:Exception(errmsg, id)
		, _type(type)
	{}

	virtual string what() const
	{
		string str = "HttpException:";
		str += _type;
		str += ":";
		str += _errmsg;
		return str;
	}

private:
	const string _type;
};

void SQLMgr()
{
	if (rand() % 7 == 0)
	{
		throw SqlException("权限不足", 100, "select * from name = '张三'");
	}
	else
	{
		cout << "SQLMgr 调用成功" << endl;
	}
}

void CacheMgr()
{
	if (rand() % 5 == 0)
	{
		throw CacheException("权限不足", 100);
	}
	else if (rand() % 6 == 0)
	{
		throw CacheException("数据不存在", 101);
	}
	else
	{
		cout << "CacheMgr 调用成功" << endl;
	}
	SQLMgr();
}

void HttpServer()
{
	if (rand() % 3 == 0)
	{
		throw HttpException("请求资源不存在", 100, "get");
	}
	else if (rand() % 4 == 0)
	{
		throw HttpException("权限不足", 101, "post");
	}
	else
	{
		cout << "HttpServer调用成功" << endl;
	}
	CacheMgr();
}
int main()
{
	srand(time(0));
	while (1)
	{
		this_thread::sleep_for(chrono::seconds(1));

		try
		{
			HttpServer();
		}
		catch (const Exception& e) // 这里捕获基类，基类对象和派生类对象都可以被捕获
		{
			// 多态调用
			cout << e.what() << endl;
		}
		catch (...)
		{
			cout << "Unkown Exception" << endl;
		}
	}

	return 0;
}

void _SendMsg(const string& s)
{
	if (rand() % 2 == 0)
	{
		throw HttpException("网络不稳定，发送失败", 102, "put");
	}
	else if (rand() % 7 == 0)
	{
		throw HttpException("你已经不是对象的好友，发送失败", 103, "put");
	}
	else
	{
		cout << "发送成功" << endl;
	}
}
// 网络不稳定，要求重试3次，均失败
void SendMsg(const string& s)
{
	for (size_t i = 0; i < 4; i++)
	{
		try
		{
			_SendMsg(s);

			// 走到这里代表成功了，跳出循环
			break;
		}
		catch (const Exception& e)
		{
			if (e.getid() == 102)
			{
				if (i == 3)
					throw;

				cout << "开始第" << i + 1 << "重试" << endl;
			}
			else
			{
				// 重新抛出异常
				//throw e;
				throw;
			}
		}
	}
}

int main()
{
	srand(time(0));
	string str;
	while (cin >> str)
	{
		try
		{
			SendMsg(str);
		}
		catch (const Exception& e)
		{
			cout << e.what() << endl << endl;
		}
		catch (...)
		{
			cout << "Unkown Exception" << endl;
		}
	}

	return 0;
}

double Divide(int a, int b)
{
	// 当b == 0时抛出异常
	if (b == 0)
	{
		throw "Division by zero condition!";
	}
	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。
	// 所以这里捕获异常后并不处理异常，异常还是交给外层处理，这里捕获了再
	// 重新抛出去。
	int* array = new int[10];

	int len, time;
	cin >> len >> time;
	try {
	cout << Divide(len, time) << endl;
	}
	catch (...)
	{
		cout << "delete []" << array << endl;
		delete[] array;

		// 重新抛出，捕获到什么抛出什么
		throw;
	}

	cout << "delete []" << array << endl;
	delete[] array;
}

int main()
{
	try
	{
		Func();
	}
	catch (const char* errmsg)
	{
		cout << errmsg << endl;
	}
	catch (...)
	{
		cout << "Unkown Exception" << endl;
	}
	return 0;
}

double Divide(int a, int b)
{
	// 当b == 0时抛出异常
	if (b == 0)
	{
		throw "Division by zero condition!";
	}
	return (double)a / (double)b;
}
int main()
{
	int i = 2;
	cout << noexcept(Divide(1, 0)) << endl;
	cout << noexcept(Divide(1, 1)) << endl;
	cout << noexcept(Divide(0,3)) << endl;
	cout << noexcept(++i) << endl;


	return 0;
}