Arduino Library Docs

Other useful functions

There's a few useful things you can do with SD objects we'll list a few here:

  • If you just want to check if a file exists, use SD.exists("filename.txt") which will return true or false.
  • You can delete a file by calling SD.remove("unwanted.txt") - be careful! This will really delete it, and there's no 'trash can' to pull it out of.
  • You can create a subdirectory by calling SD.mkdir("/mynewdir") handy when you want to stuff files in a location. Nothing happens if it already exists but you can always call SD.exists() above first.

Also, there's a few useful things you can do with File objects:

  • You can seek() on a file. This will move the reading/writing pointer to a new location. For example seek(0) will take you to the beginning of the file, which can be very handy!
  • Likewise you can call position() which will tell you where you are in the file.
  • If you want to know the size of a file, call size() to get the number of bytes in the file.
  • Directories/folders are special files, you can determine if a file is a directory by calling isDirectory()
  • Once you have a directory, you can start going through all the files in the directory by calling openNextFile()
  • You may end up with needing to know the name of a file, say if you called openNextFile() on a directory. In this case, call name() which will return a pointer to the 8.3-formatted character array you can directly Serial.print() if you want.
This guide was first published on Jul 31, 2013. It was last updated on Jul 31, 2013. This page (Arduino Library Docs) was last updated on Nov 19, 2019.