c++ template笔记(2)模板类

 

1.自定义Stack模板类

#include <vector>
#include <stdexcept>

template <typename T>
class Stack {
private:
std::vector<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();
}
};

template <typename T>
void Stack<T>::push (T const& elem)
{
elems.push_back(elem);    // append copy of passed elem
}

template<typename T>
void Stack<T>::pop ()
{
if (elems.empty()) {
throw std::out_of_range("Stack<>::pop(): empty stack");
}
elems.pop_back();         // remove last element
}

template <typename T>
T Stack<T>::top () const
{
if (elems.empty()) {
throw std::out_of_range("Stack<>::top(): empty stack");
}
return elems.back();      // return copy of last element
}

测试

#include <iostream>
#include <string>
#include <cstdlib>
#include "stack1.hpp"

int main()
{
try {
Stack<int>         intStack;       // stack of ints
Stack<std::string> stringStack;    // stack of strings

// manipulate int stack
intStack.push(7);
std::cout << intStack.top() << std::endl;

// manipulate string stack
stringStack.push("hello");
std::cout << stringStack.top() << std::endl;
stringStack.pop();
stringStack.pop();
}
catch (std::exception const& ex) {
std::cerr << "Exception: " << ex.what() << std::endl;
return EXIT_FAILURE;  // exit program with ERROR status
}
}

由于多掉了一次pop所以报错

2.用typdef产生一个特定模板类别名

比如Stack<int>

typedef Stack<int> IntStack;
int main()
{
IntStack intStack;
intStack.push(7);
std::cout << intStack.top() << std::endl;
}

3.模板类的特化

#include <deque>
#include <string>
#include <stdexcept>
#include "stack1.hpp"

template<>
class Stack<std::string> {
private:
std::deque<std::string> elems;  // elements

public:
void push(std::string const&);  // push element
void pop();                     // pop element
std::string top() const;        // return top element
bool empty() const {            // return whether the stack is empty
return elems.empty();
}
};

void Stack<std::string>::push (std::string const& elem)
{
elems.push_back(elem);    // append copy of passed elem
}

void Stack<std::string>::pop ()
{
if (elems.empty()) {
throw std::out_of_range
("Stack<std::string>::pop(): empty stack");
}
elems.pop_back();         // remove last element
}

std::string Stack<std::string>::top () const
{
if (elems.empty()) {
throw std::out_of_range
("Stack<std::string>::top(): empty stack");
}
return elems.back();      // return copy of last element
}

基于模板类之上，对于特定类型进行重新实现，比如上面就是一个对std:: string的特例实现,内部用deque实现

测试

#include <iostream>
#include <string>
#include <cstdlib>
#include "stack2.hpp"

int main()
{
try {
Stack<int>         intStack;       // stack of ints
Stack<std::string> stringStack;    // stack of strings

// manipulate int stack
intStack.push(7);
std::cout << intStack.top() << std::endl;
intStack.pop();

// manipulate string stack
stringStack.push("hello");
std::cout << stringStack.top() << std::endl;
stringStack.pop();
stringStack.pop();
}
catch (std::exception const& ex) {
std::cerr << "Exception: " << ex.what() << std::endl;
return EXIT_FAILURE;  // exit program with ERROR status
}
}

上面Stack<std::string>使用了特化的类

4.局部特化

若模板类有两个参数，那么确定其中一个参数,另一个未确定的话，则可以说是局部特化





这些概念与c#的泛型是相同的.

5.预设模板

与局部特化概念差不多,但保留了参数，给参数设置了一个默认的类型

#include <vector>
#include <stdexcept>

template <typename T, typename CONT = std::vector<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();
}
};

template <typename T, typename CONT>
void Stack<T,CONT>::push (T const& elem)
{
elems.push_back(elem);    // append copy of passed 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();         // remove last element
}

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();      // return copy of last element
}

示例:这样如果用默认的类型，就可以少指定一个模板类的类型

#include <iostream>
#include <deque>
#include <cstdlib>
#include "stack3.hpp"

int main()
{
try {
// stack of ints:
Stack<int> intStack;

// stack of doubles which uses a std::deque<> to manage the elements
Stack<double,std::deque<double> > dblStack;

// manipulate int stack
intStack.push(7);
std::cout << intStack.top() << std::endl;
intStack.pop();

// manipulate double stack
dblStack.push(42.42);
std::cout << dblStack.top() << std::endl;
dblStack.pop();
dblStack.pop();
}
catch (std::exception const& ex) {
std::cerr << "Exception: " << ex.what() << std::endl;
return EXIT_FAILURE;  // exit program with ERROR status
}
}