Re: How do I manually instantiate template functions with -fno-implicit-templates

[Mark Mitchell <mmitchell at usa dot net>]

    Here is a test case for what I need:

    test.h:

    #include<iostream.h>

    struct test_box
	{
	void print(void) {cout << "this is a test" << endl;}
	};

    void test(test_box *);  // Just a forward declaration

It is this line that is the problem.  You should have written:

  template <class BOX> void test(BOX* the_box);

here.  A long explanation below.

    test.C:

    #include "test.h"

    template <class BOX> void test(BOX *the_box)
	{
	the_box->print();
	};

    template void test<> (test_box *);  // This is the guiding decl


    main.C:

    #include "test.h"

    main()
	{
	test_box box1;
	test(&box1);
	}

First, the use of -fno-implicit-templates makes no difference in this
particular case, so let's not worry about it.  If we look at (some of)
the symbols in each .o:

supernova% nm test.o | test-c++filt
00000000 T void test<test_box>(test_box *)

supernova% nm main.o | test-c++filt
         U test(test_box *)

We can see what's happenning.  The main.C file is trying to call a
non-template function; the test.C file defines (and causes the
instantiation of) a template function.  They don't match, according to
the Standard.  That's why the prototype should be a template
prototype, not a non-template prototype.

-- 
Mark Mitchell		mmitchell@usa.net
Stanford University	http://www.stanford.edu