异常类型变量的生命周期

传统的错误处理机制：

#include<iostream>
using namespace std;

//传统的处理机制
int my_strcopy(char* from, char* to)
{
    if (from == NULL)
        return 1;
    if (to == NULL)
        return 2;

    //拷贝场景检查
    if (*from == 'a')
        return 3;
    while (*from != '')
    {
        *to = *from;
        to ++;
        from ++;
    }
    *to = '';
    return 0;
}

int main()
{
    int ret = 0;
    char buf1[] = "abcdefg";
    char buf2[1024] = { 0 };
    ret = my_strcopy(buf1, buf2);
    if (ret != 0)
    {
        switch (ret)
        {

        case 1:
            cout << "源buf出错！" << endl;
            break;
        case 2:
            cout << "目的buf出错！" << endl;
        case 3:
            cout << "拷贝过程出错!" << endl;
        default:
            cout << "未知错误" << endl;
            break;
        }
    }
    cout << "buf2 = " << buf2 << endl;
    system("pause");

    return 0;
}

用异常解决：

#include<iostream>
using namespace std;

//传统的处理机制
//throw int 类型异常
void my_strcopy2(char* from, char* to)
{
    if (from == NULL)
        throw 1;
    if (to == NULL)
        throw 2;

    //拷贝场景检查
    if (*from == 'a')
        throw 3;
    while (*from != '')
    {
        *to = *from;
        to ++;
        from ++;
    }
    *to = '';
}
//throw char 类型异常
void my_strcopy1(char* from, char* to)
{
    if (from == NULL)
        throw "源buf出错";
    if (to == NULL)
        throw "目的buf出错";

    //拷贝场景检查
    if (*from == 'a')
        throw "copy时出错";
    while (*from != '')
    {
        *to = *from;
        to++;
        from++;
    }
    *to = '';
}
class BadSrcType{};
class BadDestType{};
class BadProcessType{};
//throw 类对象类型异常
void my_strcopy3(char* from, char* to)
{
    if (from == NULL)
        throw BadSrcType(); //会不会产生匿名对象
    if (to == NULL)
        throw BadDestType();

    //拷贝场景检查
    if (*from == 'a')
        throw BadProcessType();
    while (*from != '')
    {
        *to = *from;
        to++;
        from++;
    }
    *to = '';
}
int main()
{
    int ret = 0;
    char buf1[] = "abcdefg";
    char buf2[1024] = { 0 };

    try
    {
        my_strcopy3(buf1, buf2);
    }
    catch (int e )//变量名可以写可以不写
    {
        cout << "int类型异常" << endl;
    }
    catch (char *e)
    {
        cout << e << "char*类型异常" << endl;
    }
    //---
    catch (BadSrcType e)//是把匿名对象拷贝给e，还是e直接就是匿名对象
    {
        cout << "BadSrcType类型异常" << endl;
    }
    catch (BadDestType e)
    {
        cout << "BadDestType类型异常" << endl;
    }
    catch (BadProcessType e)
    {
        cout << "BadProcessType类型异常" << endl;
    }
    //--
    catch (...)
    {
        cout << "未知异常 " << endl;
    }
    system("pause");
    return 0;
    
}

接下来解决代码中提出的问题：

    catch (BadSrcType e)//是把匿名对象拷贝给e，还是e直接就是匿名对象

先添加完类的定义：

class BadProcessType
{
public:
    BadProcessType()
    {
        cout << "BadProcessType构造函数do 
";
    }
    BadProcessType(const BadProcessType& obj)
    {
        cout << "BadProcessType拷贝构造函数do 
";
    }

    ~BadProcessType()
    {
        cout << "BadProcessType析构函数do 
";
    }
};

结论1：如果 接受异常的时候，使用一个异常变量，则拷贝构造异常变量

接下来测试引用：

    catch (BadProcessType &e)
    {
        cout << "BadProcessType类型异常" << endl;
    }

没有拷贝新的变量

结论2：如果使用引用，会使用throw的那个对象

下面测试指针：

    catch (BadProcessType &e)
    {
        cout << "BadProcessType类型异常" << endl;
    }
    catch (BadProcessType* e)
    {
        cout << "BadProcessType类型异常" << endl;
    }

结论3：指针可以和引用和元素写在一块，但是元素和引用不能写在一块

此时抛出异常时应该抛出地址：

    if (*from == 'b')
        throw& (BadProcessType());

 此时因为析构函数已经完成，指针变成了野指针。

所以指针应当这样抛出：

    if (*from == 'c')
        throw new BadProcessType;

    catch (BadProcessType* e)
    {
        cout << "BadProcessType地址类型异常" << endl;
        delete e;
    }

略烦，所以最好选择引用来抓取异常。所有操作都自动处理。