append mode "a" query

[chet at uwovax.uwo.ca]

Thanks for the help with my append mode query. With your help and some
luck, I've figured out part of what happened, but there is still a
little mystery involved which makes it worth this final posting.

(1) first, the problem is just an MS-DOS problem; both the Sun and the
VAX C compilers run B without problem

(2) The EOF (^Z, dec 26) was introduced by an assembly language editor
that I sometimes use. When I used only MicroEMACS, program B ran
without problem on Turbo C and Small-C. Whenever I used the other
editor, the ^Z crept in (I used a third, binary, editor to confirm
these facts).

(3) For Turbo C, a simple fix was to change the mode from "a" (which by
default is "at") to "r+" and then use lseek(fp, -1, 2). This position
the file pointer just before the EOF. Note, however, that it should not
be necessary to do this!

(4) Small-C (version 2.2 on MS-DOS) does not have an fseek() function,
and I have so far been unsuccessful in my attempts to use the
substitute function, bseek(), to achieve what I did in Turbo C with
lseek().

(5) I don't know what the Turbo C compiler does, but Jim Hendrix
describes the operation of fopen() very clearly in his book on Small C,
and according to his description, the DOS EOF sign (^Z) should be
changed to -1 on opening (presumably Turbo C does the same thing), and
it should not be possible to append text after it. This is the bit of
mystery that remains.

Chet Creider
creider at csd.uwo.ca