C++ template
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 }
}