以下对我有用。参数量应在[0，100]范围内。当心，没有错误处理！
void SetAlsaMasterVolume(long volume)
{
long min, max;
snd_mixer_t *handle;
snd_mixer_selem_id_t *sid;
const char *card = "default";
const char *selem_name = "Master";
snd_mixer_open(&handle, 0);
snd_mixer_attach(handle, card);
snd_mixer_selem_register(handle, NULL, NULL);
snd_mixer_load(handle);
snd_mixer_selem_id_alloca(&sid);
snd_mixer_selem_id_set_index(sid, 0);
snd_mixer_selem_id_set_name(sid, selem_name);
snd_mixer_elem_t* elem = snd_mixer_find_selem(handle, sid);
snd_mixer_selem_get_playback_volume_range(elem, &min, &max);
snd_mixer_selem_set_playback_volume_all(elem, volume * max / 100);
snd_mixer_close(handle);
}
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