异常--C++

double Divide(int a, int b)
{
	try
	{
		// 当b == 0时抛出异常
		if (b == 0)
		{
			string s("Divide by zero conditon!");
			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<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
		{
			cout << e.what() << endl;
		} 
		catch(...)
		{
			cout << "Unkown Exception" << endl;
		}
	} 

	return 0;
}

// 下⾯程序模拟展⽰了聊天时发送消息，发送失败补货异常，但是可能在
// 电梯地下室等场景⼿机信号不好，则需要多次尝试，如果多次尝试都发
// 送不出去，则就需要捕获异常再重新抛出，其次如果不是⽹络差导致的
// 错误，捕获后也要重新抛出。
void _SeedMsg(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;
	}
}
void SendMsg(const string& s)
{
	// 发送消息失败，则再重试3次
	for (size_t i = 0; i < 4; i++)
	{
		try
		{
			_SeedMsg(s);
			break;
		} 
		catch(const Exception & e)
		{
			// 捕获异常，if中是102号错误，⽹络不稳定，则重新发送
			// 捕获异常，else中不是102号错误，则将异常重新抛出
			if (e.getid() == 102)
			{
				// 重试三次以后否失败了，则说明⽹络太差了，重新抛出异常
				if (i == 3)
					throw;

				cout << "开始第" << i + 1 << "重试" << endl;
			} 
			else
			{
				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 "Divide by zero conditon!";
	}
	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];
	try
	{
		int len, time;
		cin >> len >> time;
		cout << Divide(len, time) << endl;
	}
	catch (...)
	{
		// 捕获异常释放内存
		cout << "delete []" << array << endl;
		delete[] array;
		throw;
	}
	cout << "delete []" << array << endl;
	delete[] array;
}

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

// C++98
// 这⾥表⽰这个函数只会抛出bad_alloc的异常
void* operator new (std::size_t size) throw (std::bad_alloc);
// 这⾥表⽰这个函数不会抛出异常
void* operator delete (std::size_t size, void* ptr) throw();

// C++11
size_type size() const noexcept;
iterator begin() noexcept;
const_iterator begin() const noexcept;

double Divide(int a, int b) //noexcept
{
	// 当b == 0时抛出异常
	if (b == 0)
	{
		throw "Divide by zero conditon!";
	}
	return ((double)a / (double)b);
}

int main()
{
	try
	{
		int len, time;
		cin >> len >> time;
		cout << Divide(len, time) << endl;
	}
	catch (const char* errmsg)
	{
		cout << errmsg << endl;
	}
	catch (...)
	{
		cout << "Unkown Exception" << endl;
	}

	int i = 0;
	cout << noexcept(Divide(1, 2)) << endl;
	cout << noexcept(Divide(1, 0)) << endl;
	cout << noexcept(++i) << endl;

	return 0;
}