Understanding C++: Templates

understanding

Reference connection:

A template is a tool to implement a code reuse mechanism . The template is usually used in a larger code base for the purpose of achieving code reusability and program flexibility. It can realize type parameterization, that is, the type is defined as a parameter, thus realizing the real code reusability. Templates can be divided into two categories, one is function templates, and the other is class templates.

1. Function template:

• Single ordinary function : can only handle a set of data types.
• Function overloading : operate on different sets of data
• Single function template : can handle different data types at once, but with less code

Declaration method:

//T is a template parameter, which accepts different data types (such as int, float, etc.), and class is a keyword. You can use the keyword typename instead

classtemplate

T someFunction(T arg)

{ … … …}

Function template code:

#include <iostream>
using namespace std;


// template function
//template <class T>
template <typenameT>//class和typename都可以
T Larger(T n1, T n2)
{
    
    
    return (n1 > n2) ? n1 : n2;
}

int main()
{
    
    
    int i1 = 10, i2 = 23;
    float f1 = 3.4, f2 = 5.8;
    char c1 = 'A', c2 = 'N';

    cout << "输入两个整数:\n";
    cout << Larger(i1, i2) <<" 更大。" << endl;

    cout << "\n输入两个浮点数:\n";
    cout << Larger(f1, f2) <<" 更大。" << endl;

    cout << "\n输入两个字符:\n";
    cout << Larger(c1, c2) << " 具有较大的ASCII值。";
    return 0;
}

2. Class template

Declaration method:

//T is a template parameter, which is a placeholder for the data type used. Inside the class, the member variable var and the member function someOperation() are of type T. For the function, see if it needs a return value .

//It can be called from within the class or with an object

template class className

{

… … …

public: T var;

T someOperation(T arg);

… … …

};
Use: create class template object

className classObject;

E.g:

className classObject;

className classObject;

className classObject;

Reference Code:

#include <iostream>
using namespace std;


template <class T>
class Calculator
{
    
    
private:
    T num1, num2;
public:
    Calculator(T n1, T n2)
    {
    
    
        num1 = n1;
        num2 = n2;
    }
    void displayResult()
    {
    
    
        cout << "Numbers are: " << num1 << " and " << num2 << "." << endl;
        cout << "Addition is: " << add() << endl;//以下都是class内部调用
        cout << "Subtraction is: " << subtract() << endl;
        cout << "Product is: " << multiply() << endl;
        cout << "Division is: " << divide() << endl;
    }
    T add() {
    
     return num1 + num2; }    
    T subtract() {
    
     return num1 - num2; }    
    T multiply() {
    
     return num1 * num2; }    
    T divide() {
    
     return num1 / num2; }
    T test(){
    
    cout<<"test"<<endl; return num1;}
};
int main()
{
    
    
    Calculator<int> intCalc(2, 1);//创建类模板对象
    Calculator<float> floatCalc(2.4, 1.2);//创建类模板对象
    
    cout << "Int results:" << endl;
    intCalc.displayResult();
    
    cout << endl << "Float results:" << endl;
    floatCalc.displayResult();
    
    intCalc.test();//对象调用类模板的T成员
    return 0;
}