How to adjust the volume of a sound in OpenAL?

Question

How can I adjust the volume of a sound in the OpenAL sound library?

Answer 1

You can change the global volume by setting the gain of the listener.

void Listener::setVolume(float v)
{
    Assert::isTrue(0 <= v && v <= 1);
    alListenerf(AL_GAIN, v);
}

float Listener::getVolume()
{
    ALfloat v;
    alGetListenerf(AL_GAIN, &v);
    return v;
}

Answer 2

float newVolume = 0.4f;
alSourcef(currentSourceID, AL_GAIN, newVolume);