c++ template(4)基本技巧

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1.关键字typename

这里内部的的typename指示T::const_iterator是一个类型,而不是一个静态成员.

#include <iostream>// print elements of an STL containertemplate <typename T>void printcoll (T const& coll){    typename T::const_iterator pos;  // iterator to iterate over coll    typename T::const_iterator end(coll.end());  // end position    for (pos=coll.begin(); pos!=end; ++pos) {        std::cout << *pos << ' ';    }    std::cout << std::endl;}

2.使用this->

模板类继承后无法直接调用基类成员,需要使用this->修饰符来访问基类成员

template <typename T>class Base{public:    void exit();};template <typename T>class Derive:public Base<T>{public:    void foo()    {        this->exit();        //or        Base<T>::exit();    }};

3.模板赋值操作

默认情况下,相同类型的参数可以互相赋值,不同参数无法直接赋值.如下

        Stack<int>   intStack1,intStack2;       // stack of ints        Stack<float> floatStack;     // stack of floats        intStack1=intStack2;//ok        floatStack=intStack1;//error

重写=操作符

// assign stack of elements of type T2template <typename T2>Stack<T>& operator= (Stack<T2> const&);

实现

template <typename T> template <typename T2>Stack<T>& Stack<T>::operator= (Stack<T2> const& op2){    if ((void*)this == (void*)&op2) {    // assignment to itself?        return *this;    }    Stack<T2> tmp(op2);              // create a copy of the assigned stack    elems.clear();                   // remove existing elements    while (!tmp.empty()) {           // copy all elements        elems.push_front(tmp.top());        tmp.pop();    }    return *this;}

当然以上应用也可以使用局部特化

template <typename T, typename CONT = std::deque<T> >class Stack {  private:    CONT elems;            // elements  public:    void push(T const&);   // push element    void pop();            // pop element    T top() const;         // return top element    bool empty() const {   // return whether the stack is empty        return elems.empty();    }    // assign stack of elements of type T2    template <typename T2, typename CONT2>    Stack<T,CONT>& operator= (Stack<T2,CONT2> const&);};

4.双重模板参数

模板参数也可以是一个模板类型

template <typename T,          template <typename ELEM> class CONT = std::deque >class Stack {  private:    CONT<T> elems;         // elements  public:    void push(T const&);   // push element    void pop();            // pop element    T top() const;         // return top element    bool empty() const {   // return whether the stack is empty        return elems.empty();    }};

5.模板参数初始化

template <typename T,          template <typename ELEM> class CONT = std::deque >class Stack {  private:    CONT<T> elems;         // elements  public:    void push(T const&);   // push element    void pop();            // pop element    T top() const;         // return top element    bool empty() const {   // return whether the stack is empty        return elems.empty();    }};

看起来似乎有点晕

6.模板参数值初始化

(1)函数

template <typename T>void foo(){    //only declare    T x;    //initialize    T x=T();}

(2)类模板函数

template <typename T>class MyClass{private:    T x;public:    MyClass():x() {}};

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