A simple hello world program in Linux C++.

helloplugin.cpp

#include "plugininterface.h"

#include <iostream>

using namespace std;

class HelloPlugin : public PluginInterface {
public:
    virtual void f()
    {
        cout << "hello, world" << endl;
    }
};

extern "C" {
    PluginInterface *plugin_create()
    {
        return new HelloPlugin();
    }

    void plugin_destroy(PluginInterface *plugin)
    {
        delete plugin;
    }
}

main.cpp

#include <cstdio>
#include <cstdlib>
#include <dlfcn.h>

#include "plugininterface.h"

typedef PluginInterface *(*PluginCreate)();
typedef void (*PluginDestroy)(PluginInterface *);

int main()
{
    void *handle = dlopen("./helloplugin.so", RTLD_LAZY);
    if (handle == nullptr) {
        fprintf(stderr, "dlopen: %s\n", dlerror());
        exit(EXIT_FAILURE);
    }

    PluginCreate plugin_create = reinterpret_cast<PluginCreate>(dlsym(handle, "plugin_create"));
    if (plugin_create == nullptr) {
        fprintf(stderr, "dlsym: %s\n", dlerror());
        exit(EXIT_FAILURE);
    }

    PluginDestroy plugin_destroy = reinterpret_cast<PluginDestroy>(dlsym(handle, "plugin_destroy"));
    if (plugin_destroy == nullptr) {
        fprintf(stderr, "dlsym: %s\n", dlerror());
        exit(EXIT_FAILURE);
    }

    PluginInterface *plugin = plugin_create();
    plugin->f();
    plugin_destroy(plugin);

    dlclose(handle);
    exit(EXIT_SUCCESS);
}

Makefile

CXX=g++
CFLAGS=-Wall -Wextra -O3

all: hello helloplugin.so

hello: main.cpp plugininterface.h
	$(CXX) $(CFLAGS) -ldl $< -o $@

helloplugin.so: helloplugin.cpp plugininterface.h
	$(CXX) $(CFLAGS) -shared -fPIC $< -o $@ 

clean:
	rm -f hello helloplugin.so

plugininterface.h

#ifndef PLUGININTERFACE_H
#define PLUGININTERFACE_H

class PluginInterface {
public:
    virtual void f() = 0;
    virtual ~PluginInterface() {}
};

#endif // PLUGININTERFACE_H