shared libraray

[Kevin Su]

Hi,

    I recently tried to create a shared library.  I found that if  I
compile the source with  g++, instead of gcc, symbol of functions in the
shared library can not be found with dlsym(), it returns NULL with an
error from dlerror().  With gcc, everything is working fine.

To test it, I wrote two sample file, xxx.c and test.c,  shown below.
Compiling these two files using gcc like the following will work:

$ gcc -fpic -c xxx.c
$ ld -shared xxx.o -o xxx.so
$ gcc test.c -ldl
$ a.out
xxxxxxxx

Compiling these two files using g++ like the following will NOT work:

$ g++ -fpic -c xxx.c
$ ld -shared xxx.o -o xxx.so
$ g++ test.c -ldl
$ a.out
dlsym:/tmp/xxx.so: undefined symbol: xxx


Any help or hint on this problem is much appreciated.

                Thanks,

                                        Kevin


file "xxx.c" ( the file to be built into a shared library):
====================================================

#include <stdio.h>
void
xxx(void)
{
         fprintf(stderr, "xxxxxxxx\n");
}


file "test.c" (the file that loads the shared library) :
=====================================================

#include <dlfcn.h>
#include <stdio.h>
typedef void (*func)(void);

int main()
{
        void* ptr;
        func f;

        void* handle;

        if((handle = dlopen("/tmp/xxx.so", RTLD_LAZY)) == 0){
            fprintf(stderr, "dlopen:%s\n", dlerror());
            return 0;

        if((ptr = dlsym(handle, "xxx")) == 0){
            fprintf(stderr,"dlsym%s\n", dlerror());
            return 0;
        }

        f = (func)ptr;
        f();
}