NetNews Usenet Archive 1992 #19/NN_1992_19.iso/spool/comp/lang/cplus/13299

Text File | 1992-09-04 | 3.3 KB | 120 lines

Newsgroups: comp.lang.c++
Path: sparky!uunet!mcsun!sunic!ugle.unit.no!sigyn.idt.unit.no!bjornmu
From: [e-mail] (Bj|rn P. Munch)
Subject: Re: Problem with templates...
Message-ID: <[e-mail]>
Sender: [e-mail] (NetNews Administrator)
Organization: Div. of CS & Telematics, Norwegian Institute of Technology
References:  <[e-mail]>
Date: Fri, 4 Sep 92 15:48:25 GMT
Lines: 108

In article <[e-mail]>, [e-mail] (Neelakantan Sundaresan) writes:
|>
|> I am trying to separate compile template definitions and use.
|> For instance,
|>  file1.c has
|>  -----
|>
|> #include <stdio.h>
|> #include <stdarg.h>
|> #include "file1.h"
|>
|> template <class T> XT<T>::Xtest(T t)
|> { printf("HEE\n");
|>   return 0;
|> }
|> template <class T> XT<T>::XT(){}
|>
|>  file2.c has
|>  ------
|>
|> #include <stdio.h>
|> #include <stdarg.h>
|> #include "file1.h"
|>
|> main()
|> {
|>   typedef XT<int> Y;
|>   Y x;
|>   x.Xtest(4);
|> }
|>
|>   file1.h has
|>   -------
|>
|> template <class T> class XT {
|>  public:
|>    XT();
|>    Xtest(T);
|> };
|>
|>
|> ------------ On compiling with g++ and linking I get the error
|>  undefined symbol:
|>      ___t2XT1Zi
|>          _Xtest__t2XT1Zii
|>
|> But if I have file1.c and file2.c in the same file, everything seems
|> to be okay.
|>
|>
|> Any ideas as to what is going on?
|> thanks
|> Neel.

Yes, I've been struggling with a similar problem.  I assume you want
to have the member functions compiled in file.c only.

Well, that does not happen.  You "instantiate" the template in
file2.c, but there the compiler doesn't have the definitions (bodies)
of the member functions available.  In file.c it's the opposite; you
have the body templates, but don't create any instances of them.

What you need to do, is to #include file1.c also into file2.c; then it
should work.

You'll have to include file.c also into all other files that use
instances of XT.  If you want to avoid this, and have the functions
for XT<int> compiled only in one file (but use it in other files), try
this:

In file1.h, say:

> #ifdef __GNUG__
> #pragma interface
> #endif

I'm not 100% sure that is required, but what _is_ required, is to
include this in the .c file where you want to create the functions:

> #ifdef __GNUG__
> #pragma implementation "file1.h"
> #endif
> #include  "file1.c"

This will make g++ spit out global functions, not local (static) ones.
You can use this file to instantiate all the XT's you need, e.g. by:

> typedef XT<int>  intXT;
> typedef XT<float>  floatXT;
> typedef XT<char *>  strXT;

, and you will have all the functions made for you.  In other files,
you can use these by including file1.h, but you don't have to include
file1.c too.

Hope this was comprehensible?  My earlier post about the same topic
was probably too cryptic, sorry.   :-|

Disclaimer: I haven't read this in docs, but found it out "the hard
way".  Works for me with g++ v 2.2.2 on a Sun4 running SunOS 4.1.2.

- BugWriter

---
Bj|rn P. Munch               | Dept. of Comp. Science & Telematics,
[e-mail]   | Norwegian Institute of Technology (NTH),
PhD Student                  | N-7034 Trondheim, Norway
Univeristy of Trondheim      | Fingerable addr:  [e-mail]