类模板使用示例（四） 缺省模板实参

Stack3.h的内容如下：

#ifndef STACK3_H
#define STACK3_H

#include <iostream>
#include <vector>
#include <stdexcept>

template <typename T, typename CONT = std::vector<T> >
class Stack
{
private:
    CONT elems;
public:
    void push(T const&);
    void pop();
    T top() const;
    bool empty() const
    {
        return elems.empty();
    }
};

template <typename T, typename CONT>
void Stack<T, CONT>::push(T const& elem)
{
    elems.push_back(elem);
}

template <typename T, typename CONT>
void Stack<T, CONT>::pop()
{
    if (elems.empty())
    {
        throw std::out_of_range("Stack<>::pop(): empty stack");
    }

    elems.pop_back();
}

template <typename T, typename CONT>
T Stack<T, CONT>::top() const
{
    if (elems.empty())
    {
        throw std::out_of_range("Stack<>::top(): empty stack");
    }

    return elems.back();
}

#endif // STACK3_H

测试文件main.cpp的内容如下：

#include <iostream>
#include <string>
#include <deque>
#include <cstdlib>
#include "Stack3.h"

using namespace std;

int main()
{
   try
    {
        Stack<int> intStack;// vector<int>
        intStack.push(7);
        cout << intStack.top() << endl;
        intStack.pop();

        Stack<string> stringStack;// vector<string>
        stringStack.push("Hello World");
        cout << stringStack.top() << endl;

        Stack<double, deque<double> > doubleStack;// deque<double>
        doubleStack.push(11.12);
        cout << doubleStack.top() << endl;
        doubleStack.pop();
        doubleStack.pop();
    }
    catch (std::exception const& ex)
    {
        cerr << "Exception: " << ex.what() << endl;
        return EXIT_FAILURE;// n stdlib.h
    }

    return 0;
}

结果：