loading shared libraries with same function names

[Michele]

I'm loading a couple of shared libraries into my tcl script (using the
"load" command rather than the "package require")
Both libraries have identical function names: Version
Is there a way that I can specify which library's "Version" call to
use? I don't own the library source code.

[wiede...@googlemail.com]

try this: ( no guarantee )
load lib_a.so
rename Version A::Version
load lib_b.so
rename Version B::Version

uwe

[George Peter Staplin]

If Version is a C function in both .dll or .so, then here's an example
of one way of solving that. I don't think you can use Tcl's load in
this situation. But you could duplicate some of its functionality.

$ cat symbols.c
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>

int (*version) (void);
int (*version2) (void);

int main() {
void *l, *l2;
char *err;

l = dlopen("./version.so", RTLD_NOW);
if(NULL == l) {
fprintf(stderr, "%s\n", dlerror());
return EXIT_FAILURE;
}

dlerror();
version = dlsym(l, "version");
err = dlerror();
if (err) {
fprintf(stderr, "%s\n", err);
return EXIT_FAILURE;
}

l2 = dlopen("./version2.so", RTLD_NOW);
if(NULL == l2) {
fprintf(stderr, "%s\n", dlerror());
return EXIT_FAILURE;
}

dlerror();
version2 = dlsym(l2, "version");
err = dlerror();
if (err) {
fprintf(stderr, "%s\n", err);
return EXIT_FAILURE;
}

printf("version %d\n", version());
printf("version2 %d\n", version2());

return EXIT_SUCCESS;
}

$ cat version.c
int version (void) {
return 123;
}

$ cat version2.c
int version (void) {
return 456;
}

$ gcc symbols.c -ldl
$ gcc -shared version.c -o version.so
$ gcc -shared version2.c -o version2.so

$ ./a.out
version 123
version2 456

To do what Tcl does:

int (*theext_init) (Tcl_Interp *interp);
char *err;

dlerror();
theext_init = dlsym(somelibhandle, "Theext_Init");
err = dlerror();
if (err) {
/* handle missing Theext_Init() */
}

if (TCL_OK != theext_init(interp)) {
/* print an error or return one to Tcl. Tcl_GetStringResult(interp)
is one way of getting a char * for the error message. */
return TCL_ERROR;
}

For Windows you would need LoadLibrary() and friends. You can probably
gather a lot of the patterns from the Tcl sources.

George