第十六周阅读项目：异常处理和命名空间

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1.代码：

#include <iostream >using namespace std;int a[10]= {1,2, 3, 4, 5, 6, 7, 8, 9, 10};int fun( int i);int main(){    int i ,s=0;    for( i=0; i<=10; i++)    {        try        {            s=s+fun(i);        }        catch(int)        {            cout<<"数组下标越界!"<<endl;        }    }    cout<<"s="<<s<<endl;    return 0;}int fun( int i){    if(i>=10)        throw i;    return a[i];}

运行结果：

学习心得：

try块是检查语句，throw用来当出现异常时发出的一个异常信号，而catch用来捕捉异常信息。

2.代码：

#include <iostream>using namespace  std;namespace CounterNameSpace{int upperbound;int lowerbound;class counter{    int count;public:    counter(int n)    {        if (n <= upperbound )        {            count = n;        }        else        {            count = upperbound;        }    }    void reset(int n)    {        if (n < upperbound)        {            count = n;        }    }    int run()    {        if (count > lowerbound)        {            return count--;        }        else            return lowerbound;    }};}int main(){    CounterNameSpace::upperbound = 100;    CounterNameSpace::lowerbound = 0;    CounterNameSpace::counter ob1(10);    int i;    do    {        i = ob1.run();        cout << i << " ";    }    while (i > CounterNameSpace::lowerbound);    cout << endl;    CounterNameSpace::counter ob2(20);    do    {        i = ob2.run();        cout << i << " ";    }    while (i > CounterNameSpace::lowerbound);    cout << endl;    ob2.reset(100);    do    {        i = ob2.run();        cout << i << " ";    }    while (i > CounterNameSpace::lowerbound);    cout << endl;    return 0;}

运行结果：

学习心得：

命名空间的作用是建立一些相互分隔的作用域，把一些全局实体分隔开来，以免产生名字冲突。ob2.reset(100);因为100==upperbound，所以i==0，所以直接输出0；

3.代码：

#include <iostream>using namespace  std;namespace CounterNameSpace{int upperbound;int lowerbound;class counter{    int count;public:    counter(int n)    {        if (n <= upperbound )        {            count = n;        }        else        {            count = upperbound;        }    }    void reset(int n)    {        if (n < upperbound)        {            count = n;        }    }    int run()    {        if (count > lowerbound)        {            return count--;        }        else            return lowerbound;    }};}int main(){    using CounterNameSpace::upperbound;    upperbound = 100;   //(a)    CounterNameSpace::lowerbound = 0;  //(b)    CounterNameSpace::counter ob1(10);    int i;    do    {        i = ob1.run();        cout << i<<" ";    }    while( i > CounterNameSpace::lowerbound);    cout << endl;    using namespace CounterNameSpace;    counter ob2(20);    do    {        i = ob2.run();        cout << i<<" ";    }    while( i > CounterNameSpace::lowerbound); //(c)    cout << endl;    ob2.reset(100);    lowerbound = 90;   //(d)    do    {        i = ob2.run();        cout << i <<" ";    }    while( i > lowerbound);    return 0;}

运行结果：

学习心得：

a，c，d处可以省去CounterNameSpace::，b处不可以省去CounterNameSpace::。因为using CounterNameSpace::upperbound;声明了upperbound为命名空间成员，而lowerbound没有声明，所以不能省略。在用using声明后，在其后程序中出现的upperbound，lowerbound就是隐含的指CounterNameSpace::upperbound，CounterNameSpace::lowerbound，所以c，d处可以省略。

4.代码：

#include <iostream>using namespace std;void f();class T{public:    T( )    {        cout<<"constructor"<<endl;        try        {            throw "exception";        }        catch(char*)        {            cout<<"exception"<<endl;        }        throw "exception";    }    ~T( )    {        cout<<"destructor";    }};int main(){    cout<<"main function"<< endl;    try    {        f( );    }    catch(char *)    {        cout<<"exception2"<<endl;    }    cout<<"main function"<<endl;    return 0;}void f( ){    T t;}

运行结果：

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