Hello, all ...

I've been doing templates for years (either using others' templates or making my own), but this is the first time I need to make a library that implements a template class. Here is my sample:

template1.h

// class templates
#include <iostream>

template < class T > class pair
{
private:
T a, b;
public:
pair (T first, T second);
T getmax ();
};

template_total.cpp

// class templates
#include <iostream>
#include "templates1.h"

template < class T > pair< T >::pair( T first, T second )
{
a=first; b=second;
}

template < class T > T pair< T >::getmax ()
{
T retval;
retval = a>b? a : b;
return retval;
}

int main ()
{
pair <int> myobject ( 100, 75 );
std::cout << myobject.getmax() << std::endl;
return 0;
}

... now when I compile this with gcc4.0.1 (on Mac OSX 10.4.7), this is what I get:

PugsleyButt:~/devstuff/c++/templates jmzorko$ c++ templates_total.cpp -o templates_total
PugsleyButt:~/devstuff/c++/templates jmzorko$ ./templates_total
100

... which is correct. Now I want to make a library with the template class and implementation, and use that library:

PugsleyButt:~/devstuff/c++/templates jmzorko$ cat templates1.h
// class templates
#include <iostream>

template < class T > class pair
{
private:
T a, b;
public:
pair (T first, T second);
T getmax ();
};

PugsleyButt:~/devstuff/c++/templates jmzorko$ cat templates1lib.cpp
// class templates
#include <iostream>
#include "templates1.h"

template < class T > pair< T >::pair( T first, T second )
{
a=first; b=second;
}

template < class T > T pair< T >::getmax ()
{
T retval;
retval = a>b? a : b;
return retval;
}

PugsleyButt:~/devstuff/c++/templates jmzorko$ c++ -c templates1lib.cpp -o templates1lib.o
PugsleyButt:~/devstuff/c++/templates jmzorko$ ar rcs libtemplates1.a templates1lib.o
PugsleyButt:~/devstuff/c++/templates jmzorko$ ll
total 44
0 drwxr-xr-x 9 jmzorko jmzorko 306 Jul 15 04:40 .
0 drwxr-xr-x 48 jmzorko jmzorko 1632 Jul 15 04:29 ..
4 -rw-r--r-- 1 jmzorko jmzorko 2192 Jul 15 04:40 libtemplates1.a
4 -rw-r--r-- 1 jmzorko jmzorko 156 Jul 15 04:11 templates1.cpp
4 -rw-r--r-- 1 jmzorko jmzorko 149 Jul 14 17:51 templates1.h
4 -rw-r--r-- 1 jmzorko jmzorko 244 Jul 15 04:10 templates1lib.cpp
4 -rw-r--r-- 1 jmzorko jmzorko 1980 Jul 15 04:40 templates1lib.o
20 -rwxr-xr-x 1 jmzorko jmzorko 20040 Jul 15 04:34 templates_total
4 -rw-r--r-- 1 jmzorko jmzorko 340 Jul 15 04:34 templates_total.cpp
PugsleyButt:~/devstuff/c++/templates jmzorko$ nm libtemplates1.a

libtemplates1.a(templates1lib.o):
00000094 s EH_frame1
0000007c s __GLOBAL__I_templates1lib.cpp_1FD5A050_803EC32C
00000100 s __GLOBAL__I_templates1lib.cpp_1FD5A050_803EC32C.eh
00000024 s __Z41__static_initialization_and_destruction_0ii
000000d8 s __Z41__static_initialization_and_destruction_0ii.eh
U __ZNSt8ios_base4InitC1Ev
U __ZNSt8ios_base4InitD1Ev
00000140 b __ZSt8__ioinit
U ___cxa_atexit
U ___dso_handle
U ___gxx_personality_v0
0000013c S ___i686.get_pc_thunk.bx
00000000 t ___tcf_0
000000b0 s ___tcf_0.eh
PugsleyButt:~/devstuff/c++/templates jmzorko$

... well, I don't see anything that indicates that the template is in the library (libtemplate1.a), but i'll try making code that uses it anyway and see what happens:

PugsleyButt:~/devstuff/c++/templates jmzorko$ cat templates1.cpp
// class templates
#include <iostream>
#include "templates1.h"

int main ()
{
pair <int> myobject (100, 75);
std::cout << myobject.getmax();
return 0;
}
PugsleyButt:~/devstuff/c++/templates jmzorko$ c++ templates1.cpp -L. -ltemplates1 -o templates1
/usr/bin/ld: Undefined symbols:
pair<int>::getmax()
pair<int>::pair(int, int)
collect2: ld returned 1 exit status
PugsleyButt:~/devstuff/c++/templates jmzorko$

... and that's the problem -- when I put my template class and implementation in a library, I can't use them from anywhere else. I know that templates are difficult for a C++ compiler, but how do I solve this? BTW, this code fails the same way on Windows, so once I know what the real problem is and how to fix it on *nix, i'll find the MS equivalent way to fix it ...

Has anyone else run into this? I know it's a common problem ...

Regards,

John

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