One of the great features of modern C++ is templates. A template is a simple and very powerful statement in C++ that defines the operations of a class or function. Templates are parameterized features of C++. In this article, we will explain non-type parameters for the template in C++ which can be used by a professional C++ IDE that supports C++14, C++17, and over compilers.
First of all, let’s try to explain what templates are in C++.
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 and let the user may apply the same template on different types in those template operations. 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 |
In this article we will explain how to use non-type template parameters in C++.
What are non-type parameters for templates in C++?
A template has at least one template parameter.
Parameters of a template can be:
- a type template parameter,
- a non-type template parameter,
- a template template parameter (a template passed as a parameter to the template).
A non-type template parameter (aka non-type template argument) is provided within a template parameters list and it is an expression whose value can be determined at compile time. A non-type template parameter can be a constant expression, address of function or object with external linkage, or address of static class member. Generally, non-type template parameters are used to specify the sizes of class members or to initialize a class.
A non-type parameter can be one of the following types,
- An integral type
- An enumeration type
lvaluereference type- A pointer type or reference to a class object
- A pointer or reference to a function
- A pointer or reference to a class member function
std::nullptr_t- A floating point type (since C++20)
Is there an example of non-type parameters for templates in C++?
Here is a simple a non-type template parameter example,
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template <auto a> class temp { }; |
here is a integral type for a non-type parameter that used to resize a std::array in C++ so that it has n elements.
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template <int n> class mytemp { std::array<float, n> ar; }; |
and we can use this template as below,
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mytemp<100> t; |
Is there a full example of non-type parameters for templates in C++?
Here a is a full C++ example of a non-type template parameter.
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#include <iostream> #include <array> // Non-type template parameters template <int n> class mytemp { std::array<float, n> ar; }; int main() { mytemp<100> t; } |
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