file_open() opens a file for subsequent reading.

file_open(fileOpenStatus,     // file_open_status variable
          fileVar,            // file variable
          fileName,           // file name, String variable
          fileMode)           // 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 used
name_error       // file not found
open_ok          // file successfully opened
status_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"