One of the great features of modern C++ is the ability to define templates. A template is a simple and very powerful statement in C++ that defines the operations of a class or function. In this article, we will explain type parameters for the template in C++. You can download C++ here and use a professional C++ IDE and compiler to try things out for yourself.
Table of Contents
What is a template in C++?
A template is a very powerful statement in C++ that simply defines the operations of a class, a function, an alias, or a variable. It lets the user apply the same template on different types to increase code reuse. Templates are like macros in C++, except the compiler checks the types used before the template is expanded. In the compilation mechanism of a template in C++, the source code contains only a template for a function or class, but when it is compiled, the same template can be used on multiple data types.
Here is the syntax of a template:
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template < parameters > declaration |
What are type parameters for templates in C++?
A template has at least one template parameter.
The parameters of a template can be,
- type template parameter,
- non-type template parameter,
- template template parameter (a template used as a parameter).
A type template parameter (typename or class) is a type parameter key provided within a template parameters list and it is a typename or class. Thus, user may use different type names or classes for the different declarations with templates. Here is a syntax for a template that has type parameter,
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template < type_parameter_key name > declaration |
Since C++20, the type parameter is a type constraint that can be a name of a concept or a name of a concept followed by a list of template arguments <in angle brackets>, and the concept name can be optionally qualified.
Here is a syntax for a template that has type constraint,
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template < type_constraint name > declaration |
A type parameter can be one of the following types:
- typename
- class
- concept (since C++20)
Is there a typename example of type parameters for templates in C++?
Here is a typename example for the type constraint (since C++20) example below,
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template<typename typ> class my_type { // template features here }; |
and we can use this template as below,
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my_type<int> tempclass_int; |
Is there a class example of type parameters for templates in C++?
Here is a class example for the type parameter for a template.
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template<class T> class my_temp { // template features here }; |
and we can use this template as below,
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mytemp<class A> t; |
Is there a full example of type parameters for templates in C++?
Here is a full C++ example to type template parameter,
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#include <iostream> // class name as a type parameter for a template template<class T> class my_temp { // template features here T c1, c2, c3; }; // typename as a type parameter for a template template<typename typ> class my_type { // template features here typ x, y; }; // constant typename as a type parameter for a template template <typename T> const T& my_type2 { // template features here }; // a simple class declaration class myclass { }; int main() { // a class decleration with a template class my_temp< myclass > mytempclass; // a class decleration with template typenames my_type<int> tempclass_int; my_type<float> tempclass_float; my_type<double> tempclass_double; } |
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