File content as of revision 3:7f991a3d4e71:

/* 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 "SDBlockDeviceDISCOF746NG.h"
#include <stdio.h>
#include <errno.h>

DigitalOut led (LED1);

// Instantiate the Block Device for sd card on DISCO-F746NG
SDBlockDeviceDISCOF746NG 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);
    }
}