ihandle -- a number which specifies this file.
ifilename -- the output file's name (in double-quotes).
imode -- choose the mode of opening the file. imode can be a value chosen among the following:
0 - open a text file for writing
1 - open a text file for reading
2 - open a binary file for writing
3 - open a binary file for reading
fiopen opens a file to be used by the fout family of opcodes. It must be defined in the header section, external to any instruments. It returns a number, ihandle, which unequivocally refers to the opened file.
Notice that fout and foutk can use either a string containing a file pathname, or a handle-number generated by fiopen. Whereas, with fouti and foutir, the target file can be only specified by means of a handle-number.