Dynamic library dynamic attach - c

Question

EDIT found an issue, but it still needs to be solved it should be below in answers
My task is to write app based on existing files. test.c(main) randapi.c randapi.h(2 functions in here) and initapi.c(one function). "how can You use dynamic library as dynamic loaded library. Using eg9 (where i made a dynamic library and it worked fine) write app where this libraries will be attached dynamic"
here is my try with a makefile but terminal says that :failed to open when i come to run file using ./program
i have tried also version without attaching initapi.c but then it says initRand is unknown besides that make file clearly attached it
#include <stdio.h>
#include <dlfcn.h>
#include <stdlib.h>
#define ITERATIONS 1000000L
int main(int argc, char** argv)
{
long i;
long isum;
float fsum;
void *lib;
lib=dlopen("librandapi.so", RTLD_LAZY);
if (!lib)
{
printf("failed to open");
exit(1);
}
int (*getRand)(int);
float (*getSRand)();
void (*initRand)();
getRand=dlsym(lib,"getRand");
getSRand=dlsym(lib,"getSRand");
initRand=dlsym(lib,"initRand");
initRand();
isum = 0L;
for (i = 0 ; i < ITERATIONS ; i++) {
isum += ((*getRand)(10));
}
printf( "getRand() Average %d\n", (int)(isum / ITERATIONS) );
fsum = 0.0;
for (i = 0 ; i < ITERATIONS ; i++) {
fsum += ((*getSRand)());
}
printf( "getSRand() Average %f\n", (fsum / (float)ITERATIONS) );
dlclose(lib);
return 0;
}
//////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////
makefile
zad9: test.c
gcc -Wall -o zad9 test.c -ldl
librandapi.so: randapi.o initapi.o
gcc -shared -o librandapi.so randapi.o initapi.o
randapi.o: randapi.c randapi.h
gcc -c -Wall -fPIC randapi.c
initapi.o: initapi.c
gcc -c -Wall -fPIC initapi.c
//////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////
zad9: test.c initapi.c
gcc -Wall -o zad9 test.c initapi.c -ldl
librandapi.so: randapi.o initapi.o
gcc -shared -o librandapi.so randapi.o
randapi.o: randapi.c randapi.h
gcc -c -Wall -fPIC randapi.c

Answer 1

Look at this line in man 3 dlopen:
If filename contains a slash ("/"), then it is interpreted as a (relative or absolute) path‐name. Otherwise, the dynamic linker searches for the object as follows (see ld.so(8) for further details):
(and then a buch of rules that do not include the current directory nor the one where the executable is).
My guess is that you are copying librandapi.so to the current directory and that's why dlopen() cannot find it.
If that's the case, the solution is easy:
lib=dlopen("./librandapi.so", RTLD_LAZY);