传统C语言错误异常的方式

C++异常处理方式

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

异常的使用

#include<iostream>
using namespace std;

double Division(int a, int b)
{
	if (b == 0)
	{
		throw "除0错误！";
	}
	else
	{
		return double(a / b);
	}
}

void Func()
{
	int a,b;
	cin >> a >> b;
	cout << Division(a, b) << endl;
}

int main(void)
{
	try
	{
		Func();
	}
	catch (const char* errmsg)
	{
		cout << errmsg << endl;
	}
	catch (...)
	{
		cout << "未知错误" << endl;
	}

	return 0;
}

异常的重新抛出

#include<iostream>
using namespace std;

double Division(int a, int b)
{
	if (b == 0)
	{
		throw "除0错误！";
	}
	else
	{
		return double(a / b);
	}
}

void Func()
{
	int* arr = new int[10];

	int a, b;
	cin >> a >> b;
	cout << Division(a, b) << endl;
	
	cout << "delete[]" << arr << endl;
	delete[]arr;
}

int main(void)
{
	try
	{
		Func();
	}
	catch (const char* errmsg)
	{
		cout << errmsg << endl;
	}
	catch (...)
	{
		cout << "未知错误" << endl;
	}

	return 0;
}

#include<iostream>
using namespace std;

double Division(int a, int b)
{
	if (b == 0)
	{
		throw "除0错误！";
	}
	else
	{
		return double(a / b);
	}
}

void Func()
{
	int* arr = new int[10];
	try
	{
		int a, b;
		cin >> a >> b;
		cout << Division(a, b) << endl;
	}
	catch(...){
		cout << "delete[]" << arr << endl;
		delete[]arr;
		throw;
	}
	
	cout << "delete[]" << arr << endl;
	delete[]arr;
}

int main(void)
{
	try
	{
		Func();
	}
	catch (const char* errmsg)
	{
		cout << errmsg << endl;
	}
	catch (...)
	{
		cout << "未知错误" << endl;
	}

	return 0;
}

异常安全问题

自定义异常体系

#include<iostream>
#include<Windows.h>
#include<string>
using namespace std;

double Division(int a, int b)
{
	if (b == 0)
	{
		throw "除0错误！";
	}
	else
	{
		return double(a / b);
	}
}

void Func()
{
	int* arr = new int[10];
	try
	{
		int a, b;
		cin >> a >> b;
		cout << Division(a, b) << endl;
	}
	catch(...){
		cout << "delete[]" << arr << endl;
		delete[]arr;
		throw;
	}
	
	cout << "delete[]" << arr << endl;
	delete[]arr;
}

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

	virtual string what() const
	{
		return _errmsg;
	}

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 HttpServerException : public Exception
{
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;
};

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;
	}
};


void SQLMgr()
{
	srand(time(0));
	if (rand() % 7 == 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();
}

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();
}

int main()
{
	while (1)
	{
		try 
		{
			Sleep(500);
			HttpServer();
		}
		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;
		}
	}
	return 0;
}

void SeedMsg(const string& s)
{
	// 要求出现网络错误重试三次
	srand(time(0));
	if (rand() % 3 == 0)
	{
		throw HttpServerException("网络错误", 500, "get");
	}
	else if (rand() % 4 == 0)
	{
		throw HttpServerException("权限不足", 101, "post");
	}

	cout << "发送成功:" << s << endl;
}

void HttpServer()
{
	// 要求出现网络错误，重试3次
	string str = "今晚一起看电影怎么样？";
	//cin >> str;
	int n = 3;
	while (n--)
	{
		try
		{
			SeedMsg(str);

			// 没有发生异常
			break;
		}
		catch (const Exception& e)
		{
			// 网络错误 且  重试3次内
			if (e.getid() == 500 && n > 0)
			{
				continue;
			}
			else
			{
				throw e; // 重新抛出
			}
		}
	}
}

C++标准库的异常体系