基于alsa的音量控制代码

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//头文件
#include <alsa/asoundlib.h>
//类定义
class Sound {
  public:
    Sound();
    ~Sound();
    int sound_read();
    void sound_write(int);
  private:
    snd_mixer_t * mixer;
    snd_mixer_elem_t *pcm_element;
};

//初始化-----------------------------------------------------
Sound::Sound()
{
    snd_mixer_open(&mixer, 0);
    snd_mixer_attach(mixer, "default");
    snd_mixer_selem_register(mixer, NULL, NULL);
    snd_mixer_load(mixer);
    //找到Pcm对应的element,方法比较笨拙
    pcm_element = snd_mixer_first_elem(mixer);
    pcm_element = snd_mixer_elem_next(pcm_element);
    pcm_element = snd_mixer_elem_next(pcm_element);
    //
    long int a, b;
    long alsa_min_vol, alsa_max_vol;
    ///处理alsa1.0之前的bug，之后的可略去该部分代码
    snd_mixer_selem_get_playback_volume(pcm_element,
                                        SND_MIXER_SCHN_FRONT_LEFT, &a);
    snd_mixer_selem_get_playback_volume(pcm_element,
                                        SND_MIXER_SCHN_FRONT_RIGHT, &b);

    snd_mixer_selem_get_playback_volume_range(pcm_element,
                                              &alsa_min_vol,
                                              &alsa_max_vol);
    ///设定音量范围
    snd_mixer_selem_set_playback_volume_range(pcm_element, 0, 100);

}

//读音量值-----------------------------------------------------
int Sound::sound_read()
{
    long ll, lr;
    //处理事件
    snd_mixer_handle_events(mixer);
    //左声道
    snd_mixer_selem_get_playback_volume(pcm_element,
                                        SND_MIXER_SCHN_FRONT_LEFT, &ll);
    //右声道
    snd_mixer_selem_get_playback_volume(pcm_element,
                                        SND_MIXER_SCHN_FRONT_RIGHT, &lr);
    return (ll + lr) >> 1;
}

//写入音量-----------------------------------------------------
void Sound::sound_write(int leftright)
{
    //左音量
    snd_mixer_selem_set_playback_volume(pcm_element,
                                        SND_MIXER_SCHN_FRONT_LEFT,
                                        leftright);
    //右音量
    snd_mixer_selem_set_playback_volume(pcm_element,
                                        SND_MIXER_SCHN_FRONT_RIGHT,
                                        leftright);
}

//退出-----------------------------------------------------
Sound::~Sound()
{
    snd_mixer_close(mixer);
}