service_locater.cpp

#include <iostream>

class Audio
{
public:
    virtual ~Audio() {}
    virtual void playSound(int soundId) = 0;
    virtual void stopSound(int soundId) = 0;
};

class ConsoleAudio : public Audio
{
public:
    void playSound(int soundId) override
    {
        std::cout << "ConsoleAudio::playSound()" << std::endl;
    }

    void stopSound(int soundId) override
    {
        std::cout << "ConsoleAudio::stopSound()" << std::endl;
    }
};

class NullAudio : public Audio
{
public:
    void playSound(int soundId) override
    {
        std::cout << "NullAudio::playSound()" << std::endl;
    }
    void stopSound(int soundId) override
    {
        std::cout << "NullAudio::stopSound()" << std::endl;
    }
};

class Locater
{
public:
    static void initialize()
    {
        m_service = &m_nullAudio;
    }

    static Audio &getAudio()
    {
        return *m_service;
    }

    static void provide(Audio *service)
    {
        m_service = service;
    }

private:
    static Audio *m_service;
    static NullAudio m_nullAudio;
};

Audio *Locater::m_service;
NullAudio Locater::m_nullAudio;

int main()
{
    Locater::initialize();

    // before providing
    {
        Audio &audio = Locater::getAudio();
        audio.playSound(0); // NullAudio::playSound()
    }

    ConsoleAudio *consoleAudio = new ConsoleAudio();
    Locater::provide(consoleAudio);

    Audio &audio = Locater::getAudio();
    audio.playSound(0); // ConsoleAudio::playSound()
}