YJL

I just wrote a simple C program. It’s been quite a long time, at least years, my skill has become very rusty. Any tips or tricks are welcome!

Here is the code, you can also get it on Google Code:

// get-volume is a small utility for ALSA mixer volume, written for being used
// in Conky.
//
// This code is in Public Domain
//
// Reference:
//  http://www.alsa-project.org/alsa-doc/alsa-lib/index.html
//
// Author:
//  2009 Yu-Jie Lin
//
// Compile using:
//  gcc -lasound -o get-volume get-volume.c

#include <stdio.h>
#include "alsa/asoundlib.h"

const char *ATTACH = "default";
const snd_mixer_selem_channel_id_t CHANNEL = SND_MIXER_SCHN_FRONT_LEFT;
const char *SELEM_NAME = "Master";

void error_close_exit(char *errmsg, int err, snd_mixer_t *h_mixer) {
        if (err == 0)
                fprintf(stderr, errmsg);
        else
                fprintf(stderr, errmsg, snd_strerror(err));
        if (h_mixer != NULL)
                snd_mixer_close(h_mixer);
        exit(EXIT_FAILURE);
        }

int main(int argc, char** argv) {
        int err;
        long vol;
        long vol_min, vol_max;
        int switch_value;
        snd_mixer_t *h_mixer;
        snd_mixer_selem_id_t *sid;
        snd_mixer_elem_t *elem ;

        if ((err = snd_mixer_open(&h_mixer, 1)) < 0)
                error_close_exit("Mixer open error: %s\n", err, NULL);

        if ((err = snd_mixer_attach(h_mixer, ATTACH)) < 0)
                error_close_exit("Mixer attach error: %s\n", err, h_mixer);

        if ((err = snd_mixer_selem_register(h_mixer, NULL, NULL)) < 0)
                error_close_exit("Mixer simple element register error: %s\n", err, h_mixer);

        if ((err = snd_mixer_load(h_mixer)) < 0)
                error_close_exit("Mixer load error: %s\n", err, h_mixer);

        snd_mixer_selem_id_alloca(&sid);
        snd_mixer_selem_id_set_index(sid, 0);
        snd_mixer_selem_id_set_name(sid, SELEM_NAME);

        if ((elem = snd_mixer_find_selem(h_mixer, sid)) == NULL)
                error_close_exit("Cannot find simple element\n", 0, h_mixer);

        if (argc != 2)
                error_close_exit("Missing (switch|volume) as argument\n", 0, NULL);

        if (strcmp(argv[1], "volume") == 0) {
                snd_mixer_selem_get_playback_volume(elem, CHANNEL, &vol);
                snd_mixer_selem_get_playback_volume_range(elem, &vol_min, &vol_max);
                printf("%3.0f%%", 100.0 * vol / vol_max);
                }
        else if (strcmp(argv[1], "switch") == 0) {
                snd_mixer_selem_get_playback_switch(elem, CHANNEL, &switch_value);
                printf("%s", (switch_value == 1) ? "ON" : "OFF");
                }
        else if (strcmp(argv[1], "on") == 0) {
                snd_mixer_selem_get_playback_switch(elem, CHANNEL, &switch_value);
                printf("%s", (switch_value == 1) ? "ON" : "");
                }
        else if (strcmp(argv[1], "off") == 0) {
                snd_mixer_selem_get_playback_switch(elem, CHANNEL, &switch_value);
                printf("%s", (switch_value == 1) ? "" : "OFF");
                }
        else
                error_close_exit("Invalid argument. Using (switch|volume)\n", 0, NULL);

        snd_mixer_close(h_mixer);
        return 0;
        }

This code is written for being used with Conky. Before this, I had the following in my .conkyrc:

${color lightblue}Volume:$color ${exec amixer get Master | egrep -o "[0-9]+%" | head -1 | egrep -o "[0-9]*"} % $alignr${color blue}${exec amixer get Master | grep -o "\[on\]" | head -1}$color${color red}${exec amixer get Master | grep -o "\[off\]" | head -1}$color

amixer, (e)grep, and head may not consume too much resource and I have never been aware of them running background. But, one simple C program, definitely run faster and efficient than those, because it’s just written for that purpose.

I also thought of Python. I love Python, but I personally prefer compiled program if I need to make a choice. So, I decided to use C. Python is really (usually) easy to code and (almost) fun to program, but it really consumes much more memory.

With this small program, then that part become:

${color lightblue}Volume:$color ${exec ~/bin/get-volume volume}$alignr${color blue}${exec ~/bin/get-volume on}$color${color red}${exec ~/bin/get-volume off}$color