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RE: Porting from linux/unix to windows - Libtool?

From: Francesco Calimeri
Subject: RE: Porting from linux/unix to windows - Libtool?
Date: Sun, 18 Jun 2006 15:27:12 +0200

Ok, it seems that now it works.

----Original Message----
From: Ralf Wildenhues [mailto:address@hidden
Sent: Thursday, June 15, 2006 2:43 PM
To: Francesco Calimeri
Cc: address@hidden
Subject: Re: Porting from linux/unix to windows - Libtool?


> Cross-compiled from some unixy system to MinGW?
> (Sorry, I don't remember whether the problems you had here
> are already solved or not; if not, please post a pointer to
> them, or describe them, post the errors, ...)

I have a system which needs to be distributed for linux, freebsd, macOS,
windows, solaris, and who knows where else. So the code must be very
portable: just copy the code and "make". that's it. the problem is that I
cannot use autoconf/automake. And on the internet there are not so many
hints for those who need to do everything manually.


> There is no problem with doing this manually, at all.


thanks for the advices.

> Don't you want to link $(TESTPROG) against $(LIB), too?
> Then add that one the link line as dependency.  And yes, it's
> best to add the uninstalled libtool wrapper on the link line:
> that way libtool will know what to do.

nono. just in order to be clear, dynamic libraries are intended to be used
in order to have a sort of plugin functions to the system, and the users
shoud be capable to build what they need by theirselves. Everything worked
well (even for the users) with the first implementation, which relied on
libdl (dlopen, dlclose, etc..) and .so libraries under linux; but now the
beta test should end and the system needs to be working also under windows
and so on. that's it.

Thanks to your advices and those from the mingw list, to which I'm
crossposting now since the topic is exactely the same, I've obtained
something which seems to work. I post it here for two reasone:

 (i)  maybe someone else will need to do the same or something similar in
the future, I think this could be useful
 (ii) please if someoone notices something bad or wrong, or simply something
which may be improved, please tell me! :)

ok, here we are:

// file: libmyprint.C
/* aliases for the exported symbols */
// #define myprint      libmyprint_LTX_myprint

#include <iostream>
using namespace std;

/* an exported function */
extern "C" void myprint ( int number ) {
  cout << number << endl;

// file: testlibprint.C
#include <iostream>
#include <ltdl.h>

using namespace std;

int main() {
  cout << "Dynamic library test" << endl;

  int errors=0;
  errors = lt_dlinit ();

  char *libname=new char[64];

  // asking for the library name
  cout << "Please enter library name :  ";
  cin >> libname;
  cout << endl;

  // open the library
  cout << "Opening " << libname << "..." << endl;
  lt_dlhandle handle = lt_dlopenext(libname);
  if (!handle) {
    cerr << "*** Cannot open library: " << lt_dlerror() << endl;
    return 1;
  // load the symbol
  cout << "Loading symbol myprint..." << endl;
  typedef void myprint_t (int);

  // reset errors

  myprint_t * myprint = (myprint_t *) lt_dlsym(handle, "myprint");
  const char *dlsym_error = lt_dlerror();

  if (dlsym_error) {
    cerr << "*** Cannot load symbol 'myprint': " 
         << dlsym_error << '\n';
    return 1;
  // perform the calculation
  cout << "Calling my print..." << endl;
  // close the library
  cout << "Closing library..." << endl;

// file: Makefile








all: $(LIB) $(TESTPROG)

$(OLIB): $(CLIB)
        $(LIBTOOL) --mode=compile $(GCC) -g -O -c $(CLIB)

$(LIB): $(OLIB)
        $(LIBTOOL) --mode=link $(GCC) $(NOUNDEFINED) -module -g -O -o
$(LALIB) $(LOLIB) -rpath /usr/local/lib -L$(LIBLTDLPATH) -lm

        $(LIBTOOL) --mode=link $(GCC) $(NOUNDEFINED) -g -O -o
$(TESTPROG)$(EXEEXT) $(TESTPROG).C -rpath /usr/local/lib -L$(LIBLTDLPATH)
-lltdl -lm

        $(LIBTOOL) --mode=clean rm -f $(LOLIB) $(LALIB) $(LIB)
        rm -fr .libs

        $(LIBTOOL) --mode=install cp $(TESTPROG)$(EXEEXT) $(INSTALLDIR)
        $(LIBTOOL) --mode=install cp $(LALIB) $(INSTALLDIR)
        rm -f $(INSTALLDIR)/*.a

please note that:
 - this produces a cyg$(LIBNAME)-0.dll file under cygwin, a
lib$(LIBNAME)-0.dll under mingw/windows and a .so under linux, automatically
and without the need of some specific directives;
 - since there's no need to link somehow the libraries to some executable,
the .a files can be dropped;
 - it seems that the #define directive is useless (even if I thought the
 - the filename of the library MUST start with "lib" under cygwin/mingw,
unless you want to change the way the system looks up for dlls.

Hope this helps someone else in the future.

Again, if you find some errors/possible improvements please tell me.

Thank you all! :)

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