How do I specify a working directory when saving to SD card?

Question

I'm trying to datalog to a EyeFi SD card by writing to a file with a jpg extension. Here's that portion of my code so far:

// see if the directory exists, create it if not.
if( !SD.exists("/DCIM/100NIKON") ) 
{
 if( SD.mkdir("/DCIM/100NIKON") ) 
 {
 Serial.print("File directory created: ");
 } 
 else {
 error("File directory not created");
 }
}
else
{
 Serial.print("File directory exists: ");
}
// Test file
char filename[] = "DSCN0000.JPG";
if (! SD.exists(filename))
{
 logfile = SD.open(filename, FILE_WRITE); // only open a new file if it doesn't exist
}
if (! logfile)
{
 error("Couldnt create file");
}

The Arduino creates the directory, but the file is still saved to the root. I would love some help or tips on this.

Answer 1

You're creating a directory, and then not writing the file into it.

You need to change the filename to /DCIM/100NIKON/DSCN0000.JPG";

Note that SD.open() takes the full filepath to the file, not just the file*name*.

From the Arduino Docs:

The file names passed to the SD library functions can include paths separated by forward-slashes, /, e.g. "directory/filename.txt". Because the working directory is always the root of the SD card, a name refers to the same file whether or not it includes a leading slash (e.g. "/file.txt" is equivalent to "file.txt"). As of version 1.0, the library supports opening multiple files.

(emphasis mine)

• user2218339: Oooh, I was thinking that after creating a directory with mkdir, the directory will automatically become the working directory. Thanks a lot!
• Connor Wolf: @user2218339 - Nope, and as far as I can tell, there isn't even a way to change the working directory at all. It's basically hard-wired to /.