How to Instantiate a Templated Function (131014)

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 );
}