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Learn What Is A Variable Template in C++

Learn What Is A Variable Template in C++

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. In this article, we will explain Variable Template in C++ examples that can be used by a professional C++ Code Editor and compiler that supports C++14, C++17, and over. 

First of all, let’s try to explain what a C++ template is.

What is a template in C++?

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++, considered in compilation except compiler checks types used before the template is expanded in its terms. 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.

Templates are powerful entity that can be parameterized by one or more parameters. These parameters can be type template parameters, non-type template parameters, and template template parameters (parameters which are themselves templates).

What is a variable template in C++?

A variable template is used to define a family of variables or static data members. If a static data member instantiated from a static data member template, it is called as an instantiated static data member. Note that, a variable template can be introduced by a template declaration at namespace scope, where variable-declaration declares a variable.

Syntax of a Variable Template;

Where is a simple variable template example in C++?

Here is a simple variable template example that is used to define standard gravity value.

Is there a variable template instantiation example in C++?

Now, let’s use this in a template. We can define a force template (force = mass x gravity) as below,

here gravity<T> is a variable template instantiation

Is there a full variable template example in C++?

Here is a example about class template and template instantiation of this class template,

What is wrong when using a variable template in C++?

When using a variable template be sure about declared variable type, otherwise you may have wrong results or missing data. Here is the example below, it shows why you cannot use int type as an input to declare f5, f6 integer variables as below.

and the output will be as follows,

as you see f5 and f6 are the wrong values here, these options doesn’t help to get correct data from this variable template. Because our template type looks the type of the input variable that we use, so it should be float or double to use its precision side.

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About author

Dr. Yilmaz Yoru has 33+ years of coding with more than 30+ programming languages, mostly C++ on Windows, Android, Mac-OS, iOS, Linux, and some other operating systems. He was born in 1974, Eskisehir-Turkey, started coding in college and graduated from the department of Mechanical Engineering of Eskisehir Osmangazi University in 1997. He worked as a research assistant at the same university for more than 10 years. He received his MSc and PhD degrees from the same department at the same university. Since 2012, he is the founder and CEO of Esenja LLC Company. He has married and he is a father of a son. Some of his interests are Programming, Thermodynamics, Fluid Mechanics, Artificial Intelligence, 2D & 3D Designs, and high-end innovations.
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