Q131014: How to Instantiate a Templated Function

Article: Q131014
Product(s): Microsoft C Compiler
Version(s): 2.00 2.10 4.00
Operating System(s): 
Keyword(s): kbcode kbCompiler kbCPPonly kbVC
Last Modified: 29-JUL-2001

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The information in this article applies to:

- The C/C++ Compiler (CL.EXE), included with:
   - Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 4.0 
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SUMMARY
=======

There is no built-in way to create an explicit instantiation of a templated
function. Normally, an instantiation is created when the function is called the
first time with a specific type. Subsequent calls to the function with the same
type use the same piece of the code generated before. However, if you want to
instantiate the function without actually calling it, you must use one of the
methods in this article.

MORE INFORMATION
================

The best method to use with function templates is to place the function
definition in a header file, and include that header file in all of the source
files.

If this is not an option then try one of these alternatives:

- In the source file where the function is defined, explicitly reference the
  function by taking the address of the function.

-or-

- In the source file where the function is defined, add a dummy function that
  makes a call to the templated function. The dummy function itself does not
  need to be called.

NOTE: With both of these alternative methods, a prototype still needs to be
provided for all source files that might call the templated function.

Sample Code
-----------

  /* Compile options needed: none
  */ 

  /********** Source File One **********/ 
  void func1(void);
  template < class T> T SwapTemplate(T Source) {
     return Source;
  }
  void Dummy(void) {                            // Option One
     char a = 'a', b;
     b = SwapTemplate(a);
  }

  void main() {
     int (*pfunc)(int) = SwapTemplate;     // Option Two
     func1();
  }

  /********** Source File Two **********/ 

  template < class T> T SwapTemplate(T Source); // Prototype

  void func1(void) {
     int  a = 5, b;
     char c = 'c', d;
     b = SwapTemplate( a );
     d = SwapTemplate( c );
  }

Additional query words: kbinf 9.00 9.0 9.1 9.10 2.00 2.10 4.00

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Keywords          : kbcode kbCompiler kbCPPonly kbVC 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : 2.00 2.10 4.00

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