File content as of revision 2:993735af824b:

/* Example file of using SD/MMC Block device Library for MBED-OS
 * Copyright 2017 Roy Krikke
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

#include "mbed.h"
#include "FATFileSystem.h"
#include "BD_SD_DISCO_F746NG.h"
#include <stdio.h>
#include <errno.h>

DigitalOut led (LED1);

// Instantiate the Block Device for sd card on DISCO-F746NG
BD_SD_DISCO_F746NG bd;
FATFileSystem fs ("fs");

void
return_error (int ret_val) {
  if (ret_val)
    printf ("Failure. %d\r\n", ret_val);
  else
    printf ("done.\r\n");
}

void
errno_error (void* ret_val) {
  if (ret_val == NULL)
    printf (" Failure. %d \r\n", errno);
  else
    printf (" done.\r\n");
}

int
main () {
  Serial pc (SERIAL_TX, SERIAL_RX);
  pc.baud (115200);
  printf ("Start\n");

  int error = 0;
  printf ("Welcome to the filesystem example.\r\n"
          "Formatting a FAT, RAM-backed filesystem. ");
  error = FATFileSystem::format (&bd);
  return_error (error);

  printf ("Mounting the filesystem on \"/fs\". ");
  error = fs.mount (&bd);
  return_error (error);

  printf ("Opening a new file, numbers.txt.");
  FILE* fd = fopen ("/fs/numbers.txt", "w");
  errno_error (fd);

  for (int i = 0; i < 20; i++) {
    printf ("Writing decimal numbers to a file (%d/20)\r", i);
    fprintf (fd, "%d\r\n", i);
  }
  printf ("Writing decimal numbers to a file (20/20) done.\r\n");

  printf ("Closing file.");
  fclose (fd);
  printf (" done.\r\n");

  printf ("Re-opening file read-only.");
  fd = fopen ("/fs/numbers.txt", "r");
  errno_error (fd);

  printf ("Dumping file to screen.\r\n");
  char buff[16] = { 0 };
  while (!feof (fd)) {
    int size = fread (&buff[0], 1, 15, fd);
    fwrite (&buff[0], 1, size, stdout);
  }
  printf ("EOF.\r\n");

  printf ("Closing file.");
  fclose (fd);
  printf (" done.\r\n");

  printf ("Opening root directory.");
  DIR* dir = opendir ("/fs/");
  errno_error (fd);

  struct dirent* de;
  printf ("Printing all filenames:\r\n");
  while ((de = readdir (dir)) != NULL) {
    printf ("  %s\r\n", &(de->d_name)[0]);
  }

  printf ("Closeing root directory. ");
  error = closedir (dir);
  return_error (error);
  printf ("Filesystem Demo complete.\r\n");

  // Blink led with 2 Hz   
  while (true) {
    led = !led;
    wait (0.5);
  }
}