Simple usage of dlopen / dlsym / dlclose

main.c

#include <stdio.h>
#include <stdlib.h>

#include <dlfcn.h>

#define DLL_PATH_ADD "./libadd.so"
#define DLL_PATH_SUB "./libsub.so"

typedef int (*func)(int, int);

int main()
{
{
    void *dlhandler_add;

    func func_add = NULL;
    dlhandler_add = dlopen(DLL_PATH_ADD, RTLD_LAZY);
    if (NULL == dlhandler_add)
	{
        fprintf(stderr, "%s\n", dlerror());
    
		exit(-1);
    }
    dlerror();
    func_add = dlsym(dlhandler_add, "add");
	if (func_add)
		printf("%d\n", func_add(1, 2));
    dlclose(dlhandler_add);
}
{
	void *dlhandler_sub;

    func func_sub = NULL;
    dlhandler_sub = dlopen(DLL_PATH_SUB, RTLD_LAZY);
    if (NULL == dlhandler_sub)
	{
        fprintf(stderr, "%s\n", dlerror());
    
		exit(-1);
    }
    dlerror();
    func_sub = dlsym(dlhandler_sub, "sub");
	
	if (func_sub)
		printf("%d\n", func_sub(1, 2));
    dlclose(dlhandler_sub);
}
    return 0;
}

add.c

int add(int a, int b)
{
	return (a + b);
}

sub.c

int sub(int a, int b)
{
	return (a - b);
}

Makefile

all:
	gcc -g add.c -shared -fPIC -o libadd.so
	gcc -g sub.c -shared -fPIC -o libsub.so

	gcc -g main.c -rdynamic -ldl -o test
	./test

clean:
	rm -rf test *.so

The operation results are as follows

3
-1