file_open() opens a file for subsequent reading.
file_open(fileOpenStatus, // file_open_status variablefileVar, // file variablefileName, // file name, String variablefileMode) // file mode (must be read_mode)
fileOpenStatus is a variable of type file_open_status. It receives the status result of the file open operation. It's values can be
mode_error // no longer usedname_error // file not foundopen_ok // file successfully openedstatus_error // file already opened
fileVar is a variable of type file. It is the internal variable that tracks the file state. It is used in other file methods like endfile and file_close.
fileName is a string containing the file name. It must contain the complete absolute path.
fileMode is a constant of type file_mode, however at this time the value must be "read_mode"