C++ is one of the most popular programming languages worldwide. Like other programming languages, it also provides different ways to create functions to perform different tasks through the code. These functions in C++ are specific to the data type you pass in as arguments. But there might be scenarios when a programmer would need generic programming, and that’s where templates in C++ come into the picture. For instance, a programmer might need to use a sort() function to sort data of different types. Usually, the programmer would have to create and use other functions for each data type. The templates in C++ help overcome this challenge.
Templates in C++?
Templates in C++ act as the foundation of generic programming. It is a simple yet powerful tool that acts as a blueprint for creating generic functions or classes. While using a template in C++, you pass a data type as a parameter. Thus, instead of maintaining multiple codes, you have to write one code and give the data type you want to use. C++ templates use two primary keywords, ‘template’ and ‘typename,’ where the ‘typename’ can be replaced with the ‘class’ keyword.
How Do C++ Templates Work?
The templates in C++ are expanded during compile-time. At the very core, they work like macros except for a single significant difference. Unlike macros, the type checking in C++ templates is done before template expansion. This allows the compiled code to have multiple copies of the same class.
Function Templates in C++?
We use C++ function templates for creating functions that can be used with different data types. A function template is used to perform the same function on multiple data types. An alternative approach to this is using function overloading. However, using a function template is a better approach to writing less and more maintainable code.Â
The basic syntax of a function template is:
template <class type> ret-type func-name(parameter_list) {
   // body of function
}
In the above syntax, type is just a placeholder that the compiler will automatically replace with the actual data type. The keyword class in the syntax is used to specify a generic type and be replaced by a typename.
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Example: Declaring a Function Template in C++
In the below example, you must create a function template in C++ and use it to find the larger value for different data types.
#include <iostream>
using namespace std;
template <class Ttype>
Ttype MaxVal(Ttype i, Ttype j){
    return (i > j)? i: j;
}
int main(){
    cout << MaxVal<int>(5, 8) << endl; // Call myMax for int
    cout << MaxVal<double>(6.5, 4.0) << endl; // call myMax for double
    cout << MaxVal<char>('f', 'k') << endl; // call myMax for char
return 0;
}
Output
Class Templates in C++
The class templates in C++ make the class using it generic. It operates similar to function templates except that it is used on the entire class instead of a single function.
The basic syntax of declaring a class template is:
template<class type>
class class_name
{
.
.
}
Once the class is created, you can declare the data type while declaring the class instance.
Example: Declaring a Class Template in C++
#include <iostream>
using namespace std;
template <class Ttype>
class Array{
private:
Ttype *pointr;
int size;
public:
Array(Ttype arr[], int s);
void print();
};
template <class Ttype>
Array<Ttype>::Array(Ttype arr[], int s) {
pointr = new Ttype[s];
size = s;
for(int i = 0; i < size; i++)
pointr[i] = arr[i];
}
template <class Ttype>
void Array<Ttype>::print() {
for (int i = 0; i < size; i++)
cout<<" "<<*(pointr + i);
cout<<endl;
}
int main(){
int arr[5] = {1, 2, 3, 4, 5};
Array<int> a(arr, 5);
a.print();
return 0;
}
Output
Passing Multiple Arguments to Templates in C++
Like normal functions and classes, you can pass multiple data types as arguments to templates. Now, let’s look at an example that takes multiple arguments.
#include<iostream>
using namespace std;
template<class Ttype, class Utype>
class A{
Ttype x;
Utype y;
public:
A(){ cout<<"The Constructor is Called"<<endl; }
};
int main() {
A<char, char> a;
A<int, double> b;
return 0;
}
Output
How to Specify Default Arguments for Templates in C++?
Similar to normal parameters, you can specify default arguments for templates. Here’s an example to demonstrate how to specify a default argument for templates in C++.
#include<iostream>
using namespace std;
template<typename Ttype, typename Utype = char>
class Example{
public:
Ttype i;
Utype j;
Example() { cout<<"The Constructor is Called"<<endl; }
};
int main() {
Example<char> a;
return 0;
}
Output
Difference Between Function Overloading and Templates in C++
Like function overloading, templates in C++ also allow polymorphism. However, there is a fundamental difference between the two. You use the function overloading when you want to perform similar operations. On the other hand, templates in C++ are used to perform precisely identical operations on different data types.
Template Specialization?
Template specialization in C++ declares different codes or behavior for a specific data type. This means you can create a specialized version of a function when executed with a particular data type. The code depicted below demonstrates the use of template specialization in C++:
#include <iostream>
using namespace std;
template <typename Ttype>
void Example(Ttype t)
{
cout << "The standard example template: "
<< t << endl;
}
template<>
void Example(int t)
{
cout << "Specialized example template for int: "
<< t << endl;
}
int main()
{
Example<char>('x');
Example<int>(12);
Example<float>(15.30);
}
Output
As you can see in the output, the template is executed for char and float data types alike but differently for the int data type.
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Conclusion
In this article, we learned about templates in C++. We also looked into examples for both types of templates: function and class. We learned how to create templates and used them to execute with different data types.Â
If you are new to C++ programming and interested in learning about other fundamental concepts of C++, you can refer to our C++ Tutorial for Beginners. The course is specifically designed for beginners and contains guides for various basic concepts. This course will help you excel in the field of C++ programming and related concepts
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