What\'s the Deal with Non-Type Parameters in C Templates?

Non-Traditional Template Declaration: Exploring Templates with Non-Type Parameters

In the realm of C programming, we often encounter template declarations that specify type parameters, like template . However, a unique variation involves templates defined with non-type parameters, such as template .

This unconventional declaration raises several questions: what constitutes a non-type parameter? And how can templates exist without any type parameters?

Understanding Non-Type Parameters

A non-type parameter in a template refers to a value that is not a type but a compile-time constant. Types of non-type parameters include:

• Integral constant expressions (e.g., integers, enumerations)
• Pointers to objects/functions with external linkage
• References to objects/functions with external linkage

Templates with Non-Type Parameters

Templates can indeed exist without any explicit type parameters by utilizing default arguments. In such cases, default values are assigned to non-type parameters. For instance:

<code class="cpp">template<unsigned int SIZE = 3>
struct Vector {
    unsigned char buffer[SIZE];
};</code>

In this example, SIZE is a non-type template parameter with a default value of 3. When declaring an instance of the Vector struct without specifying the SIZE parameter, the default value will be used:

<code class="cpp">Vector<> test; // Size of buffer will be 3</code>

Syntactic Note

It's crucial to distinguish between an explicit template specialization (marked by template<>) and a template without parameters. The former specifies an alternative definition for a specific parameter value, while the latter has no parameters, only default values.

In conclusion, templates can extend beyond type parameters and encompass non-type parameters as well. This flexibility allows programmers to define templates with compile-time constants, pointers, and references, broadening the range of template applications and enhancing code reusability.

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