Re: file position
On Jun 30, 12:49 pm, "Alf P. Steinbach" <al...@start.no> wrote:
* James Kanze:
On Jun 30, 9:26 am, "Alf P. Steinbach" <al...@start.no> wrote:
* nko...@gmail.com:
When outputting or inputting to a file is there some easy
way to move to and overwrite a specific line?
No, not if you're talking about an ordinary text file.
If you know the length of the line, there is. You have to
save the position prior to reading the line.
You're talking about a special case where (1) you've been at
that line sometime earlier, (2) you saved the position then,
and (3) the new line is exactly the same length as the old.
There are often such rare corener special cases that are
possible for something that isn't possible in general.
It's quite misleading to put that up as if it contradicted
what I wrote.
Yes and no. I forget what you'd actually written, but it's not
important. Such cases are rare, unless you actively take steps
to create them.
That hasn't anything to do with C++, it has to do with the
structure of an ordinary text file.
Not really.
Really. ;-)
For the general problem, it's the same in any language.
Is it? Or maybe the question is: what is the general problem?
We regularly seek to arbitrary lines in files here, using the
Posix interface (which doesn't distinguish between text files
and binary files). Of course, you can't reliably do it under
Posix in an arbitrary file written with the editor; we also
write the files, and take care that all of the lines have the
same known length. I've done similar things in Fortran, in the
past. The general problem here is that the C++ language doesn't
provide an interface for this sort of things; other languages
do.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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