SdFat: counting number of files in directory?

Other Hardware Storage
1

How would I count the number of files in an SdFat directory and then access the nth file, to open or printName? Thanks.

2

This is possible but not very useful since the order of files in a FAT16/FAT32 directory is random.

Why do want to do this?

3

Thanks for prompt reply. I want to set a variable to the number of files in /LOGS directory, then display the filenames, 10 at a time, to my TFT screen. Down/Up arrows would page through the directory. Touching a file name would pass that filename to another function to display the contents of that file.

If the file order is random, why do I get the same order of listing each time I run openNext and printName, that is:

140302.CSV
140304.CSV
140314.CSV

4

By random order I mean files are created using the first free directory entry. This means you can't know where a new file will be created. Deleting a file causes the directory entry to be free.

You can use openNext() to count the files.

To open the nth file just skip files using openNext() until the nth file.

5

Yes, that would work, like this:

void ListLogs() {
int k = 0;
sd.chdir("/LOGS");
while (file.openNext(sd.vwd(), O_READ)) {
file.printName(&Serial);
k++;
Serial.println();
file.close();
}
sd.chdir("/");
Serial.print("There are ");
Serial.print(k);
Serial.println(" files in the logs directory");
}

But it would have to run through the directory once to count the files, and then repeatedly to get to the group of ten wanted. Is there a way to access the indicator that openNext uses and then open the nth file?

6

No.

Since used directory entries are randomly scattered through the directory file you can't seek to the nth used entry.

openNext() just sequentially reads the directory file.

7

OK, thanks.