C++ function template introduction

Introduction of function templates

Generally speaking, when we write a function, its parameter types are determined. For example, the following function prototype:

void Swap(int &a,int &b);

As you can see from the function prototype, this is a swap function. The function is to exchange the incoming values of a and b.
But we can also see that the parameters passed in are all of int type, so only two int values can be exchanged.
So the question is: If I pass two double variables, do I have to write another function (of course, using function overloading can indeed reflect the polymorphism of C++), but what about other types? long, sort, long long...
So we need to introduce another concept- template to achieve such a function, so that we only write a function to complete the input of all generic parameters.

Function template keyword-template

The keyword of the function template is-template

template <typename AnyType>
void Swap(AnyType &a,AnyType &b)
{
    
    
	AnyType temp;
	temp=a;
	a=b;
	b=temp;
}

As you can see from the above code, a generic type is defined by the keyword template and defined by the keyword typename , where AnyType is just a name, any C++ canonical naming, such as "T" (and this naming is also more Common) can also

template <typename T>

example

Now we, through an example to see the definition and use of the template function

#include<iostream>
using namespace std;
template <typename T>
void Swap(T &a,T &b);

int main()
{
    
    
	int i=10;
	int j=20;
	cout<<"i，j="<<i<<"，"<<j<<".\n";
	cout<<"Using compiler generated int swapper:\n";
	Swap(i,j);
	cout<<"Now i，j="<<i<<"，"<<j<<".\n";
	
	double x=24.5;
	double y=81.7;
	cout<<"x，y="<<x<<"，"<<y<<".\n";
	cout<<"Using compiler generated double swapper:\n";
	Swap(x,y);
	cout<<"Now x，y="<<x<<"，"<<y<<".\n";
	return 0;
}

template <typename T>
void Swap(T &a,T &b)
{
    
    
	T temp;
	temp=a;
	a=b;
	b=temp;
}

After running, the output: As
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you can see, the Swap function is called twice, once with int type and once with double type, but only one function is written, which saves a lot of code

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Reference book: "C++ Primer Plus 6th"