20_异常

异常

int ret = 0;
try
{
    //throw 1;
    //throw 'A';
    throw 2.14f;
}
catch(int e)
{
    cout << "int异常值为: " << e << endl;
}
catch(char e)
{
    cout << "char异常值为: " << e << endl;
}
catch(...) //捕获所有异常
{
    cout << "其他异常值为: " << endl;
}

栈解旋

异常被抛出后，从进入try块起，到异常被抛掷前，这期间在栈上构造的所有对象，都会被自动析构。析构的顺序与构造的顺序相反,这—过程称为栈的解旋.

try
{
    Data ob1;
    Data ob2;
    Data ob3;
    throw 1; //抛出异常后 ob3 ob2 ob1 依次自动释放(栈解旋)
}
catch(int e)
{
    cout << "int异常值为: " << e << endl;
}
catch(char e)
{
    cout << "char异常值为: " << e << endl;
}
catch(...)
{
    cout << "其他异常值为: " << endl;
}

先释放对象再捕获异常

异常的接口声明

异常的接口声明: 可以抛出哪些类型的异常

函数默认 可以抛出任何类型的异常(推荐)

void fun()
{
    throw 1; //ok
    throw '1'; //ok
    throw "hello"; //ok

只抛出特定类型的异常

void fun02() throw(int, char)
{
	throw 1; //ok
	throw '1'; //ok
	throw "hello"; //抛出 不能捕获
}

不能抛出任何异常

void fun03() throw()
{
    throw 1; //不能抛出
    throw 'o'; //不能抛出
    throw "dfj"; //不能抛出
}

异常变量的生命周期

以普通对象接异常值

以对象指针 接异常值

try
{
    throw new MyException;
}
catch(MyException *e) //指针对象接异常(delete释放)
{
    cout << "普通对象接异常" << endl;
    delete e;
}

对象引用接异常值(推荐)

try
{
    throw MyException();
}
catch(MyException &e)
{
    cout << "普通对象接异常" << endl;
}

异常的多态

//异常基类
class BaseException
{
public:
    virtual void printError(){};
};

//空指针异常
class NullPointerException: public BaseException
{
public:
    virtual void printError()
    {
        cout << "空指针异常!" << endl;
    }
};

//越界异常
class OutOfRangException: public BaseException
{
public:
    virtual void printError()
    {
        cout << "越界异常!" << endl;
    }
};

void doWork()
{
    //throw NullPointerException();
    throw OutOfRangeException();
}

int main()
{
    try
    {
        doWork();
    }
    catch(BaseException& ex) //父类引用 可以捕获搭配该父类派生出的所有子类的子类
    {
        ex.printError();
    }
}

C++标准异常

try
{
    throw out_of_range("哈哈, 我越界了");
    //throw bad_alloc();
}
catch(exception &e)
{
    //what()存放的是异常信息(char *方式存在)
    cout << e.what() << endl;
}

编写自己的异常

基于标准异常基类 编写自己的异常类

#include <iostream>

using namespace std;

class NewException: public exception
{
private:
    string msg;
public:
    NewException(){}
    NewException(string msg)
    {
        this->msg = msg;
    }
    //重写父类的what
    virtual const char* what() const throw() //防止父类在子类前抛出标准异常
    {
        //将string转换成char*
        return this->msg.c_str();
    }
    ~NewException(){}
};

int main()
{
    try
    {
        throw NewException("哈哈, 自定义异常");
    }
    catch(exception &e)
    {
        cout << e.what() << endl;
    }
    return 0;
}