* Chris Bowlby wrote on Thu, Oct 21, 2004 at 10:00:33PM CEST:
> Hi All,
>
> I've been working on a project for some time now and am working into the
> system a means of creating dynamic modules that will need to be loaded via
> dlopen (will use libltdl once I've got my initial testing done - for
> portability reasons), my sample code is as follows:
>
> #include <dlfcn.h>
> #include <unistd.h>
>
> #include <iostream>
>
> void main(void) {
> void (*test_function) (int &);
See below.
> void *handle;
>
> handle = dlopen("libtest/libtest.la", RTLD_NOW);
This will not work. lt_dlopen can open .la files, dlopen can only open
the corresponding shared objects, most likely called libtest.so (or
similar with version numbers) on your system.
> if (!handle) {
> cerr << dlerror() << "\n";
This will not work in ISO C++.
using namespace std;
or similar will be necessary.
> exit(EXIT_FAILURE);
Better include stdlib.h (or, FWIW, cstdlib) for exit().
> }
>
> // test_function = dlsym(handle, "test_fun");
>
> dlclose(handle);
> }
>
> There are two issues that I've come up with, during compile time with the:
>
> test_function = dlsym(handle, "test_fun");
>
> uncommented it complains about:
>
> test.cxx: In function 'void main(void)':
> test.cxx:17: ANSI C++ forbids implicit conversion from 'void *' in
> assignment
This has nothing to do with libtool, and everything with C++ type
safety. You have to cast the return value of dlsym to the correct type.
> The second issue is that dlopen (when I get the system to compile the
> program by commenting out the dlsym line) complains that libtest/libtest.la
> is not of the right format, I'm compiling it using:
>
> lib_LTLIBRARIES: libtest.la
Typo: you want
lib_LTLIBRARIES = libtest.la
> libtest_la_SOURCES = test.cxx
> libtest_la_LDFLAGS = -module
The last and (to me) most interesting issue: apart from the fact that in
C, already conversion from void pointer to function pointer is
undefined, is there any ISO C++ reason against conversion to a C++
function pointer (like test_function above)? I don't think so, but I'm
not really sure.
Regards,
Ralf
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