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C ++ template

Templates are generic programming, generic programming that is a stand-alone manner to any particular type of writing code.

Template to create a generic class or function blueprint or formula. Library containers, iterators, and algorithms for example, are examples of generic programming, they all use the concept of templates.

Each container has a single definition, such asvectors, we can define a number of different types of vectors, such as vector <int>orvector <string>.

You can use templates to define the functions and classes, let's take a look at how to use.

Function template

The general form of the template function is defined as follows:

template <class type> ret-type func-name(parameter list)
{
   // 函数的主体
}  

Here, type is a function of the data types used placeholder names. The name can be used in the function definition.

Here is an example of a function template returns the maximum number of two kinds:

#include <iostream>
#include <string>

using namespace std;

template <typename T>
inline T const& Max (T const& a, T const& b) 
{ 
    return a < b ? b:a; 
} 
int main ()
{
 
    int i = 39;
    int j = 20;
    cout << "Max(i, j): " << Max(i, j) << endl; 

    double f1 = 13.5; 
    double f2 = 20.7; 
    cout << "Max(f1, f2): " << Max(f1, f2) << endl; 

    string s1 = "Hello"; 
    string s2 = "World"; 
    cout << "Max(s1, s2): " << Max(s1, s2) << endl; 

   return 0;
}

When the above code is compiled and executed, it produces the following results:

Max(i, j): 39
Max(f1, f2): 20.7
Max(s1, s2): World

Class template

As we define function templates, we can define the class templates. The general form of a generic class declaration is as follows:

template <class type> class class-name {
.
.
.
}

Here, type is a placeholder type name can be specified in the class is instantiated.You can use a comma-separated list to define multiple generic data types.

The following example defines a class Stack <>, and implements the generic approach to stack pop operations on elements:

#include <iostream>
#include <vector>
#include <cstdlib>
#include <string>
#include <stdexcept>

using namespace std;

template <class T>
class Stack { 
  private: 
    vector<T> elems;     // 元素 

  public: 
    void push(T const&);  // 入栈
    void pop();               // 出栈
    T top() const;            // 返回栈顶元素
    bool empty() const{       // 如果为空则返回真。
        return elems.empty(); 
    } 
}; 

template <class T>
void Stack<T>::push (T const& elem) 
{ 
    // 追加传入元素的副本
    elems.push_back(elem);    
} 

template <class T>
void Stack<T>::pop () 
{ 
    if (elems.empty()) { 
        throw out_of_range("Stack<>::pop(): empty stack"); 
    }
	// 删除最后一个元素
    elems.pop_back();         
} 

template <class T>
T Stack<T>::top () const 
{ 
    if (elems.empty()) { 
        throw out_of_range("Stack<>::top(): empty stack"); 
    }
	// 返回最后一个元素的副本 
    return elems.back();      
} 

int main() 
{ 
    try { 
        Stack<int>         intStack;  // int 类型的栈 
        Stack<string> stringStack;    // string 类型的栈 

        // 操作 int 类型的栈 
        intStack.push(7); 
        cout << intStack.top() <<endl; 

        // 操作 string 类型的栈 
        stringStack.push("hello"); 
        cout << stringStack.top() << std::endl; 
        stringStack.pop(); 
        stringStack.pop(); 
    } 
    catch (exception const& ex) { 
        cerr << "Exception: " << ex.what() <<endl; 
        return -1;
    } 
}  

When the above code is compiled and executed, it produces the following results:

7
hello
Exception: Stack<>::pop(): empty stack