Re: [ooc-compiler] Help With I/O

[Michael v. A. <Mic...@de...>]

Gregory Gelfond <gre...@tt...> writes:

> Hello All,
> 
> I am completely new to Oberon, and am attempting to learn the language.  I
> understand the basics of the language as described in Wirth's book, but am
> having some difficulty in learning the oo2c library.  I have the following
> program:
> 
> MODULE DisplayFile;
> [...]
> 
> I have several difficulties running this program.  The program displays the
> contents of the file "HelloWorld.Mod", with the exception of the last line.
> How can I specify the termination condition of the loop to read "While not
> end of file do"?

Using your program (plus fix), I see all the lines from the input file
duplicated to stdout -- as expected.  "WHILE res=done DO" should
definitely work.

> Also, can someone explain the meaning of the third parameter 'res' of the
> Files.Old function call?

Opening the file may file.  A "res#done" indicates an error.  This
should be checked.  For example, when I started your program without
providing the input file, I got a seg fault because `file' was NIL.
`res' would indicate a "file not found" error.

> Furthermore, in Wirth's book, the I/O functions that are described differ
> from those present in the oo2c library.  Am I correct in understanding that
> these are the ones defined in the Oakwood modules?  If so, what are the
> benefits/drawbacks of one over the other?

In general, the resemblance between the libraries of oo2c and the
original documentation of the Oberon System is superficial.  By
necessity, any I/O library put on top of the standard C/POSIX library
needs to decide whether to implement its own view of the world, or to
provide a faithful representation of the low-level functions of the
operating system (or C library).  In a way, the Wirth I/O functions
_are_ the operating system.  OOC leans more in the direction of the
operating system it is using, which is represented by the I/O
functions of C.  For example, the v2 compiler comes with a set of
low-level IO modules (like IO:FileChannel and IO:SocketChannel) that
are essentially one-to-one interfaces to C's open(), read(), write(),
etc.

As for Oakwood: The v1 compiler distribution has a set of Oak* modules
that are closer to the original Oberon System modules.

-- mva