关键字explict、template<class T>

题目名称 : [Exception] Stack and Exception

时间限制 : 1000 ms

空间限制 : 32 MB

Description

【The point of problem is exception】

Implement the definition of class Stack(last in first out).

const int MAX_LEN = 5;

template<class T>

class Stack

{

public:

explicit Stack();

bool empty() const;

int size() const;

T& top();

const T& top() const;

void push(const T& x);

void pop();

private:

T data[MAX_LEN];

int stack_size;

};

The max capacity of the Stack is 5. When there are five elements in the Stack, we should follow the rule if we want to push a new element into stack:

Assume the top element of the Stack is b, the new element is a:

1) if a > b, remove the top element and push the new element into Stack

2) if a <= b, do nothing.

when executing operation pop(), it should throw a double exception if there is no element in the Stack. when executing operation top(), it should throw a int exception if there is no element in the Stack. Like the following program:

Stack<int> s;

try {

s.top();

} catch (int) {

cout << "get top failed" << endl;

}

try {

s.pop();

} catch (double) {

cout << "pop failed" << endl;

}

【Sample Out】

The output should be：

get top failed

pop failed

代码：

Stack.h:

#ifndef Stack_and_Exception_Stack_h

#define Stack_and_Exception_Stack_h

const int MAX_LEN = 5;

template<class T>

class Stack {

  public:

    explicit Stack(): stack_size(0) {}/*关键字explicit，可以阻止不应该允许的经过转换构造函数进行的隐式转换的发生。声明为explicit的构造函数不能在隐式转换中使用。*/

    bool empty() const {

        return stack_size == 0;

   
4000
}

    int size() const {

        return stack_size;

    }

    T& top();

    const T& top() const;

    void push(const T& x);

    void pop();

    operator bool() const {return !empty();}

  private:

    T data[MAX_LEN];

    int stack_size;

};

template<class T>

T& Stack<T>::top() {

    if (empty())

        throw 1;

    return data[stack_size - 1];

}

template<class T>

const T& Stack<T>::top() const {

    if (empty())

        throw 1;

    return data[stack_size - 1];

}

template<class T>

void Stack<T>::pop() {

    if (empty())

        throw 1.0;

    stack_size--;

}

template<class T>//每步实现之前都要加上这一句

void Stack<T>::push(const T& x) {

    if (stack_size == MAX_LEN) {

        if (!(top() < x))

            return;

        stack_size--;

    }

    data[stack_size++] = x;

}

#endif

main.cpp

#include "Stack.h"

#include <iostream>

using namespace std;

int main() {

    Stack<int> s;

    cout << s.size() << endl;

    for (int i = 10; i < 15; i++) {

        s.push(i);

        cout << s.size() << endl;

    }

    cout << s.size() << endl;

    s.push(12);

    cout << s.top() << endl;

    cout << s.size() << endl;

    s.push(16);

    cout << s.top() << endl;

    cout << s.size() << endl;

    for (int i = 5; i >= 0; i--) {

        try {

            cout << s.top() << endl;

        }

        catch(int int_e) {

            cout << "get top failed" << endl;

        }

        try {

            s.pop();

        }

        catch(double dou_e) {

            cout << "pop failed" << endl;

        }

        cout << s.size() << endl;

    }

    for (int i = 10; i < 15; i++) {

        s.push(i);

        cout << s.size() << endl;

        cout << s.top() << endl;

    }

    return 0;

}

知识点1、template<class T>

template <class 类型参数名>,template意思是“模板

用类模板定义对象的方法与此相似，但是不能直接写成
   Compare cmp(4,7); // Compare是类模板名
Compare是类模板名，而不是一个具体的类，类模板体中的类型numtype并不是一个实际的类型，只是一个虚拟的类型，无法用它去定义对象。必须用实际类型名去取代虚拟的类型，具体的做法是：
    Compare <int> cmp(4,7);

eg:

#include <iostream>
using namespace std;
template <class numtype>
//定义类模板
class Compare
{
public :
Compare(numtype a,numtype b)
{x=a;y=b;}
numtype max( )
{return (x>y)?x:y;}
numtype min( )
{return (x<y)?x:y;}
private :
numtype x,y;
};
int main( )
{
Compare<int > cmp1(3,7); //定义对象cmp1，用于两个整数的比较
cout<<cmp1.max( )<<" is the Maximum of two integer numbers."<<endl;
cout<<cmp1.min( )<<" is the Minimum of two integer numbers."<<endl<<endl;
Compare<float > cmp2(45.78,93.6); //定义对象cmp2，用于两个浮点数的比较
cout<<cmp2.max( )<<" is the Maximum of two float numbers."<<endl;
cout<<cmp2.min( )<<" is the Minimum of two float numbers."<<endl<<endl;
Compare<char> cmp3(′a′,′A′); //定义对象cmp3，用于两个字符的比较
cout<<cmp3.max( )<<" is the Maximum of two characters."<<endl;
cout<<cmp3.min( )<<" is the Minimum of two characters."<<endl;
return 0;
} 上面列出的类模板中的成员函数是在类模板内定义的。如果改为在类模板外定义，不能用一般定义类成员函数的形式：
    numtype Compare::max( ) {…} //不能这样定义类模板中的成员函数
而应当写成类模板的形式：
    template <class numtype>
    numtype Compare<numtype>::max( )
    {
        return (x>y)?x:y;
    }

 类模板的类型参数可以有一个或多个，每个类型前面都必须加class，如：
    template <class T1,class T2>
    class someclass
    {…};
在定义对象时分别代入实际的类型名，如：
    someclass<int,double> obj;