STM32 and SDFat - Can't create file in directory in SD

Question

I'm using the SdFat.h library on a STM32 and I can successfully create a file in the root directory using SD.open("test.txt", FILE_WRITE); but my code fails to create SD.open("DATA/data_test.txt", FILE_WRITE); in a directory. Here's the piece of code that successfully creates a file in the root:

String final_book_name = upload_book_name + ".txt";
if (SD.exists(final_book_name.c_str())) {
  SD.remove(final_book_name.c_str());
}
tft.println(final_book_name); // This successfully prints "test.txt"
book_file = SD.open(final_book_name, FILE_WRITE);
if (SD.exists(final_book_name.c_str())) {
  tft.print("Created file");
} else {
  tft.print("Failed to create/replace\nfile!");
}

and here's the piece of the code that fails to create a file in a directory:

if (!SD.exists(DATA_DIR)) {
  SD.mkdir(DATA_DIR);
}
String final_book_name = upload_book_name + ".txt";
String book_data_path = DATA_DIR;
book_data_path += "/data_" + final_book_name;
if (SD.exists(book_data_path.c_str())) {
  SD.remove(book_data_path.c_str());
}
tft.println(book_data_path); // This successfully prints "DATA/data_test.txt"
File book_data_file = SD.open(book_data_path, FILE_WRITE);
if (SD.exists(book_data_path.c_str())) {
  book_data_file.print(upload_book_font);
  book_data_file.print("|");
  book_data_file.print("0");
  book_data_file.close();
} else{
  tft.print("Failed to create/replace\ndata file!");
  if (SD.exists(final_book_name.c_str())) {
    SD.remove(final_book_name.c_str());
  }
}

Answer 1

I found the issue. I'm not creating the directory folder properly. When I checked the SD card from another device, the DATA folder was invalid, and creating it manually works. I'll look for a solution and post an update.

UPDATE: https://forum.arduino.cc/index.php?topic=421131.0 I'll try this tomorrow but it'll probably fix the issue.

Answer 2

As you have given no variable for DATA_DIR

String book_data_path = DATA_DIR;
book_data_path += "/data_" + final_book_name;

so your resulting path looks like

DATA_DIR + "/data_" + final_book_name

IF DATA_DIR = "/" then it would be "/" + "/data_" + final_book_name

As tip do not use the string class but char arrays

definition

 const char[] DATA_DIR = "/books";  
 char book_data_path [128] = {'\0'};
 char final_book_name [13] =  {'\0'}; // IF no LFN support is used its 8.3 !!!
 const char upload_book_name[] = "my_book";
 strcpy (final_book_name, upload_book_name);
 strcat (final_book_name, ".txt");
 Serial.println(final_book_name);

If you want long filr namesupport us SDFat library or enable LFB withSD lib (whichneeds about 35% ,ore memory as SDfat (when using long file names).
EDIT
As you are using SDFat and I do not know which version/fork there is abug with writing to subdirectories. Please check the following:
To check run the SdFat\examples\DirectoryFunctions and watch your serial monitor for the results
SdFile.cpp. At line 782 and 1452, you have (in my version):

if (block <= m_vol->cacheBlockNumber()
  && block < (m_vol->cacheBlockNumber() + nb)) {

The working code has:

if (m_vol->cacheBlockNumber() <= block
  && block < (m_vol->cacheBlockNumber() + nBlock)) {

If you have the upper version change it and it should work
EDIT 2 Work around for buggy SDFat lib
Here is a workaround code

const char DATA_DIR [] = "data";
char final_book_name[128] ={'\0'};
char book_data_path [256] ={'\0'};

if (!SD.exists(DATA_DIR)) {
  SD.mkdir(DATA_DIR);
  SD.chdir(DATA_DIR);
}

strcpy (final_book_name, upload_book_name);
 strcat (final_book_name, ".txt";
String book_data_path = DATA_DIR;

strcpy(book_data_path, "data_");
strcat(book_data_path, final_book_name);

if (SD.exists(book_data_path)) {
  SD.remove(book_data_path);
}
SD.mkdir(book_data_path);
SD.chdir(book_data_path);

tft.println(DATA_DIR);
tft.println(book_data_path); // This successfully prints "DATA/data_test.txt"
File book_data_file = SD.open(final_book_name, FILE_WRITE);
if (SD.exists(final_book_name)) {
  book_data_file.print(upload_book_font);
  book_data_file.print("|");
  book_data_file.print("0");
  book_data_file.close();
} else{
  tft.print("Failed to create/replace\ndata file!");
  if (SD.exists(final_book_name)) {
    SD.remove(final_book_name);
  }
}