# Cannot open file with underscores using the SD library

So I'm trying to create a new file that has underscores in its name. However, when I try this, no file is created.

This works

String fileName = "NMEA.txt";
mySensorData = SD.open(fileName.c_str(), FILE_WRITE);


This does not work

String fileName = "NMEA__23_33_3__16_7_29.txt";
mySensorData = SD.open(fileName.c_str(), FILE_WRITE);


Does anyone know why?

• I tried String fileName = "/23_33_3/16_7_29/NMEA.txt" to organize it by directory and it doesn't seem to create them. – Zoom Bee Jul 30 '16 at 0:22