Song list code module

Collect MP3 song list from the SD card

Reference Articles

Get a list of MP3 files (naive way)

The objective of this code is to get a list of *.mp3 files at the root directory of your SD card.

#include "ff.h"

void print_list_of_mp3_songs(void) {
  FRESULT result;
  FILINFO file_info;
  const char *root_path = "/";

  DIR dir;
  result = f_opendir(&dir, root_path);

  if (result == FR_OK) {
    while (1) {
      result = f_readdir(&dir, &file_info);

      const bool item_name_is_empty = (file_info.fname[0] == 0);
      if ((result != FR_OK) || item_name_is_empty) {
        break; /* Break on error or end of dir */
      }

      const bool is_directory = (file_info.fattrib & AM_DIR);
      if (is_directory) {
        /* Skip nested directories, only focus on MP3 songs at the root */
      } else { /* It is a file. */
        printf("Filename: %s\n", file_info.fname);
      }
    }
    f_closedir(&dir);
  }
}

Get list of MP3 songs

Here is a better way to design code such that a dedicated code module will obtain song-list for you:

// @file: song_list.h

#pragma once

#include <stddef.h> // size_t

typedef char song_memory_t[128];

/* Do not declare variables in a header file */
#if 0
static song_memory_t list_of_songs[32];
static size_t number_of_songs;
#endif

void song_list__populate(void);
size_t song_list__get_item_count(void);
const char *song_list__get_name_for_item(size_t item_number);

#include <string.h>

#include "song_list.h"

#include "ff.h"

static song_memory_t list_of_songs[32];
static size_t number_of_songs;

static void song_list__handle_filename(const char *filename) {
  // This will not work for cases like "file.mp3.zip"
  if (NULL != strstr(filename, ".mp3")) {
    // printf("Filename: %s\n", filename);

    // Dangerous function: If filename is > 128 chars, then it will copy extra bytes leading to memory corruption
    // strcpy(list_of_songs[number_of_songs], filename);

    // Better: But strncpy() does not guarantee to copy null char if max length encountered
    // So we can manually subtract 1 to reserve as NULL char
    strncpy(list_of_songs[number_of_songs], filename, sizeof(song_memory_t) - 1);

    // Best: Compensates for the null, so if 128 char filename, then it copies 127 chars, AND the NULL char
    // snprintf(list_of_songs[number_of_songs], sizeof(song_memory_t), "%.149s", filename);

    ++number_of_songs;
    // or
    // number_of_songs++;
  }
}

void song_list__populate(void) {
  FRESULT res;
  static FILINFO file_info;
  const char *root_path = "/";

  DIR dir;
  res = f_opendir(&dir, root_path);

  if (res == FR_OK) {
    for (;;) {
      res = f_readdir(&dir, &file_info); /* Read a directory item */
      if (res != FR_OK || file_info.fname[0] == 0) {
        break; /* Break on error or end of dir */
      }

      if (file_info.fattrib & AM_DIR) {
        /* Skip nested directories, only focus on MP3 songs at the root */
      } else { /* It is a file. */
        song_list__handle_filename(file_info.fname);
      }
    }
    f_closedir(&dir);
  }
}

size_t song_list__get_item_count(void) { return number_of_songs; }

const char *song_list__get_name_for_item(size_t item_number) {
  const char *return_pointer = "";

  if (item_number >= number_of_songs) {
    return_pointer = "";
  } else {
    return_pointer = list_of_songs[item_number];
  }

  return return_pointer;
}

int main(void) {
  song_list__populate();
  for (size_t song_number = 0; song_number < song_list__get_item_count(); song_number++) {
    printf("Song %2d: %s\n", (1 + song_number), song_list__get_name_for_item(song_number));
  }
}