C++类模板的特化（三）

本文主要介绍类模板的特化、局部特化和缺省模板实参；

1.类模板的特化

类模板的特化（Class Template Specialization）是指为特定的模板参数提供自定义实现的过程。通过特化，我们可以针对某些特定的类型或条件提供不同的行为或实现；

如果需要特化一个类模板，需要特化该模板中的所有成员函数；

模板的特化注意事项：
需要将模板写成template <>，并且需要指明特定的类型，下面示例需要特化std::string的类型，成员函数按照正常的函数实现即可

template <>
class Stack <std::string>
{}

示例

/** @brief: class complates* @complie: g++ -g *.cc -o d -std=c++11* @autor: your name* @date: 2023/08/22*/#include <iostream>
#include <vector>
#include <stdexcept>template <class T>
class Stack 
{
private:std::vector<T> elems;public:void push(T const&);void pop();T top() const;bool empty() const{return elems.empty();}    int32_t getElemsSize() const{std::cout<<"not string size"<<std::endl;return elems.size();}
};template <typename T>
void Stack<T>::push(T const& elem)
{elems.push_back(elem);
}template <typename T>
void Stack<T>::pop()
{if(elems.empty()) {throw std::out_of_range("empty stack");}elems.pop_back();
}template <typename T>
T Stack<T>::top() const
{if(elems.empty()) {throw std::out_of_range("empty stack");}return elems.back();
}//std::string
template <>
class Stack <std::string>
{
private:std::vector<std::string> elems;public:void push(std::string const&);void pop();std::string top() const;bool empty() const{return elems.empty();}    int32_t getElemsSize() const{std::cout<<"string size"<<std::endl;return elems.size();}
};void Stack<std::string>::push(std::string const& elem)
{elems.push_back(elem);
}void Stack<std::string>::pop()
{if(elems.empty()) {throw std::out_of_range("empty stack");}elems.pop_back();
}std::string Stack<std::string>::top() const
{if(elems.empty()) {throw std::out_of_range("empty stack");}return elems.back();
}int main(int argc, char* argv[])
{Stack<int> int_stack;int_stack.push(10);int_stack.push(20);int_stack.push(30);std::cout<<int_stack.getElemsSize()<<std::endl;//std::stringStack<std::string> string_stack;string_stack.push("class");string_stack.push("int");string_stack.push("int64");string_stack.push("double");string_stack.push("float");std::cout<<string_stack.getElemsSize()<<std::endl;return 0;
}

2. 类模板的局部特化

类模板的局部特化（Partial Class Template Specialization）是指针对模板参数的部分特化，只针对某些特定的条件进行自定义实现的过程。通过局部特化，我们可以为满足特定条件的模板参数提供不同的实现。

示例

/** @brief: class complates* @complie: g++ -g *.cc -o d -std=c++11* @autor: your name* @date: 2023/08/22*/#include <iostream>
#include <vector>
#include <stdexcept>
#include <string>//局部特化
template <typename T, typename U>
class MyClass
{
public:void print() const{std::cout<<"typename and typename"<<std::endl;}
};template <typename T>
class MyClass<T, std::string>
{
public:void print() const{std::cout<<"typename and string"<<std::endl;}
};template <typename T>
class MyClass<T, double>
{
public:void print() const{std::cout<<"typename and double"<<std::endl;}
};int main(int argc, char* argv[])
{MyClass<int, int> int_myclass;int_myclass.print();MyClass<int, std::string> string_myclass;string_myclass.print();MyClass<int, double> double_myclass;double_myclass.print();return 0;
}

输出

typename and typename
typename and string
typename and double

3. 缺省模版实参

在函数模板的时候，可以将模板的参数定位为缺省值；即支持默认，也支持指定，使用起来更加的方便；

示例

/** @brief: class complates* @complie: g++ -g *.cc -o d -std=c++11* @autor: your name* @date: 2023/08/22*/#include <iostream>
#include <vector>
#include <deque>
#include <stdexcept>
#include <string>//缺省模版参数
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();}    int32_t getElemsSize() const{        return elems.size();}
};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("empty stack");}elems.pop_back();
}template <typename T, typename CONT>
T Stack<T, CONT>::top() const
{if(elems.empty()) {throw std::out_of_range("empty stack");}return elems.back();
}int main(int argc, char* argv[])
{//使用默认值Stack<int> int_stack;int_stack.push(10);int_stack.push(20);int_stack.push(30);std::cout<<int_stack.top()<<std::endl;//赋值类型Stack<double, std::deque<double>> double_stack;double_stack.push(10.11);double_stack.push(20.22);double_stack.push(30.33);std::cout<<double_stack.top()<<std::endl;return 0;
}

输出

30
30.33