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Opens a file on the SD card. If the file is opened for writing, it will be created if it doesn't already exist (but the directory containing it must already exist).

Syntax, mode)


filename: the name the file to open, which can include directories (delimited by forward slashes, /) - char *

mode (optional): the mode in which to open the file, defaults to FILE_READ - byte. one of:

  • FILE_READ: open the file for reading, starting at the beginning of the file.
  • FILE_WRITE: open the file for reading and writing, starting at the end of the file.


a File object referring to the opened file; if the file couldn't be opened, this object will evaluate to false in a boolean context, i.e. you can test the return value with "if (f)".

See also

Reference Home

Corrections, suggestions, and new documentation should be posted to the Forum.

The text of the Arduino reference is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.