File content as of revision 4:73e7dc25c9be:

/* 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>

// Instantiate the Block Device for sd card on DISCO-F746NG
SDBlockDeviceDISCOF746NG bd;
FATFileSystem fs ("fs");


int
main ()
{

    printf("Start\n");

    int error = 0;
    printf("Welcome to the filesystem example.\r\n"
           "Formatting a FAT, RAM-backed filesystem. ");
    error = FATFileSystem::format(&bd);
    
    printf("Mounting the filesystem on \"/fs\". ");
    error = fs.mount(&bd);
    //Write to file and create if not exist
    printf("Opening a new file, numbers.txt.");
    FILE* fd = fopen("/fs/numbers.txt", "w");
    
    //Printing to file
    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");

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

    //close stream
    fclose(fd);
    printf("Closing file.");
}