ALSA lib--简单的control使用例子

代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>
#include <alsa/asoundlib.h>
#include <unistd.h>

int ctl_val(char *card, char *elem_name, int set_val, int elem_value)
{
    snd_ctl_t * handle;
    snd_ctl_elem_info_t *info;
    snd_ctl_elem_id_t *id;
    snd_ctl_elem_value_t *value;
    snd_ctl_elem_list_t *list;
    snd_ctl_elem_type_t *type;
    unsigned int count, used, idx, info_count;
    int err;
    long tmp;
    long long tmp64;

    err = snd_ctl_open(&handle, card, 0);
    if (err < 0) {
        printf("%s(), L%d  err: %s\n", __FUNCTION__, __LINE__, snd_strerror(err));
        return err;
    }
    
    snd_ctl_elem_info_alloca(&info);
    snd_ctl_elem_id_alloca(&id);
    snd_ctl_elem_value_alloca(&value);
    snd_ctl_elem_list_alloca(&list);

    err = snd_ctl_elem_list(handle, list);
    if (err < 0) {
        printf("%s(), L%d  err: %s\n", __FUNCTION__, __LINE__, snd_strerror(err));
        return err;
    }

    count = snd_ctl_elem_list_get_count(list);
    used = snd_ctl_elem_list_get_used(list);
    while(count != used) {
        err = snd_ctl_elem_list_alloc_space(list, count);
        if (err < 0) {
            printf("%s(), L%d  err: %s\n", __FUNCTION__, __LINE__, snd_strerror(err));
            return err;
        }
        err = snd_ctl_elem_list(handle, list);
        if (err < 0) {
            printf("%s(), L%d  err: %s\n", __FUNCTION__, __LINE__, snd_strerror(err));
            return err;
        }
        used = snd_ctl_elem_list_get_used(list);
    }

    for (idx = 0; idx < used; idx++)
        if (!strcmp(snd_ctl_elem_list_get_name(list, idx), elem_name))
            break;
    }
    
    if (idx >= used) {
        printf("%s(), L%d  idx: %d, used:%d\n", __FUNCTION__, __LINE__, idx, used);
        return -1;
    }

    snd_ctl_elem_list_get_id(list, idx, id);
    snd_ctl_elem_info_set_id(info, id);

    err = snd_ctl_elem_info(handle, info);
    if (err < 0) {
        printf("%s(), L%d  err: %s\n", __FUNCTION__, __LINE__, snd_strerror(err));
        return err;
    }
    
    snd_ctl_elem_info_get_id(info, id);
    snd_ctl_elem_value_set_id(value, id);

    err = snd_ctl_elem_read(handle, value);
    if (err < 0) {
        printf("%s(), L%d  err: %s\n", __FUNCTION__, __LINE__, snd_strerror(err));
        return err;
    }

    type = snd_ctl_elem_info_get_type(info);
    info_count = snd_ctl_elem_info_get_count(info);
    for (idx = 0; idx < info_count && idx < 128; idx++) {
        switch(type) {
            case SND_CTL_ELEM_TYPE_BOOLEAN:
                tmp = snd_ctl_elem_value_get_boolean(value, idx);
                printf("%s(), L%d  %s idx:%d, tmp:%ld\n", __FUNCTION__, __LINE__, elem_name, tmp);
                if (set_val)
                    snd_ctl_elem_value_set_boolean(value, idx, elem_value);
                break;
            case SND_CTL_ELEM_TYPE_INTEGER:
                tmp = snd_ctl_elem_value_get_integer(value, idx);
                printf("%s(), L%d  %s idx:%d, tmp:%ld\n", __FUNCTION__, __LINE__, elem_name, tmp);
                if (set_val)
                    snd_ctl_elem_value_set_integer(value, idx, elem_value);
                break;
            case SND_CTL_ELEM_TYPE_INTEGER64:
                tmp64 = snd_ctl_elem_value_get_integer64(value, idx);
                printf("%s(), L%d  %s idx:%d, tmp64:%lld\n", __FUNCTION__, __LINE__, elem_name, tmp64);
                if (set_val)
                    snd_ctl_elem_value_set_integer64(value, idx, elem_value);
                break;
            case SND_CTL_ELEM_TYPE_ENUMERATED:
                tmp = snd_ctl_elem_value_get_enumerated(value, idx);
                printf("%s(), L%d  %s idx:%d, tmp:%ld\n", __FUNCTION__, __LINE__, elem_name, tmp);
                if (set_val)
                    snd_ctl_elem_value_set_enumerated(value, idx, elem_value);
                break;
            case SND_CTL_ELEM_TYPE_BYTES:
                tmp = snd_ctl_elem_value_get_byte(value, idx);
                //tmp = snd_ctl_elem_value_get_bytes(value);
                printf("%s(), L%d  %s idx:%d, tmp:%ld\n", __FUNCTION__, __LINE__, elem_name, tmp);
                if (set_val)
                    snd_ctl_elem_value_set_bytes(value, &elem_value, sizeof(elem_value));
                break;
            default:
                break;
        }
    }
    
    if (set_val) {
        err = snd_ctl_elem_write(handle, value);
        if (err < 0) {
            printf("%s(), L%d  err: %s\n", __FUNCTION__, __LINE__, snd_strerror(err));
            return err;
        }
    }

    return 0;
}

int main(int argc, char **argv)
{
    int err = 0;
    char *card = NULL;
    char *elem_name = NULL;
    int elem_value = 0;
    int set_val = 0;

    if (argc < 3)
        return -1;
    card = argv[1];
    elem_name = argv[2];
    if (argc >= 4) {
        elem_value = atoi(argv[3]);
        set_val = 1;
    }
    return ctl_val(card, elem_name, set_val, elem_value);
}