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 explain how to use type template parameter without a default 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 |
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).
What is a type template parameter without a default in C++?
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,
In general, when we declare a template we use type template parameter without a default, this is the most general usage of type parameter in templates.
Here is the syntax for the template parameter without a default.
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template < type_parameter_key name(optional) > declaration |
A type parameter can be one of the following types,
- typename
- class
- concept (since C++20)
For example we can declare a template as below,
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template<class T> class my_temp { }; |
Is there a C++ example of using a type template parameter without a default?
Here is an example to the template parameter without a default.
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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; }; // a simple class declaration class myclass { }; int main() { // a class declaration with a template class my_temp< myclass > mytempclass; } |
Is there a C++ VCL example of a type template parameter without a default?
Here is a full C++ VCL console example of using a template parameter without a default in C++ Builder.
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#include <vcl.h> // Type Name Parameter for Class Template // class name as a type parameter for a template template<class T> class my_temp { // template features here T c1, c2, c3; }; // a simple class declaration class myclass { }; int _tmain(int argc, _TCHAR* argv[]) { // a class decleration with a template class my_temp< myclass > mytempclass; } |
Here is a full Windows VCL Application C++ Builder example of a template parameter without a default.
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#include <fmx.h> #pragma hdrstop #include "Unit1.h" //--------------------------------------------------------------------------- #pragma package(smart_init) #pragma resource "*.fmx" TForm1 *Form1; // Type Name Parameter for Class Template // class name as a type parameter for a template template<class T> class my_temp { // template features here T c1, c2, c3; }; // a simple class declaration class myclass { }; //--------------------------------------------------------------------------- __fastcall TForm1::TForm1(TComponent* Owner) : TForm(Owner) { // a class declaration with a template class my_temp< myclass > mytempclass; } |
Is there a C++ FMX example of using a type template parameter without a default?
Here is a full C++ FMX console example of using a template parameter without a default in C++ Builder.
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#include <fmx.h> // Type Name Parameter for Class Template // class name as a type parameter for a template template<class T> class my_temp { // template features here T c1, c2, c3; }; // a simple class declaration class myclass { }; int _tmain(int argc, _TCHAR* argv[]) { // a class declaration with a template class my_temp< myclass > mytempclass; } |
Finally, here is a full Windows FMX Application C++ Builder example of a template parameter without a default.
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#include <fmx.h> #pragma hdrstop #include "Unit1.h" //--------------------------------------------------------------------------- #pragma package(smart_init) #pragma resource "*.fmx" TForm1 *Form1; // Type Name Parameter for Class Template // class name as a type parameter for a template template<class T> class my_temp { // template features here T c1, c2, c3; }; // a simple class declaration class myclass { }; //--------------------------------------------------------------------------- __fastcall TForm1::TForm1(TComponent* Owner) : TForm(Owner) { // a class declaration with a template class my_temp< myclass > mytempclass; } |
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