sterretje:
No, it's not walking down the wrong path. It's open source; if the author decides not to fix it, you can fix it.
In my experience, if I think the library should be modified, I'm probably thinking wrong. (i.e. My code is faulty.) I've only ever had to do this once, and it was for something way outside of "passing a variable".
sterretje:
It more than likely does not work because the filename in the code that you posted does not adhere to the 8.3 convention.
Apologies for the typo in the file, I had been heavily modifying it all day yesterday to try various iterations and hit an extra 0 when I was cleaning it up for posting. Wasn't seeing straight.
sterretje:
PS
Which version of the IDE do you use? On which operatings system? Which version of the SD library is reported?
IDE v1.8.7, Win 7, SD v1.2.2
Nevertheless ... it turned out the problem was in EEPROM.update() of all things. It wasn't writing, and so the fileName logic wasn't generating the filename correctly, so it was giving filenames of "SWDL_00-255.txt", which obviously isn't 8.3. Switching to a forced .put() instead fixed the issue. I'll add a remove() call to mitigate any future issues.
I've already let them know not to use it more than 50k times, and not for longer than a month of continuous use. (This is totally reasonable.)
I still can't figure out why I can't use the Serial port at the same time as the SD card, but that's not important enough to try and solve.