Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!hsdndev!cmcl2!adm!news
From: CDCKAB%EMUVM1.BITNET@cunyvm.cuny.edu ( Karl Brendel)
Newsgroups: comp.lang.pascal
Subject: Re: Selective write within files
Message-ID: <26391@adm.brl.mil>
Date: 28 Mar 91 15:58:38 GMT
Sender: news@adm.brl.mil
Lines: 62

In article <1991Mar27.160905.1962@cs.mcgill.ca>, storm@cs.mcgill.ca
  (Marc WANDSCHNEIDER) wrote:

>Say I have the following file (assigned to TEST.TXT):
>
>-->
>This is a nice little file that has a few lines of straight ASCII
>text that I wish to manipulate.
>After I've written this program, I will then print it out, and give
>a copy to my friend <INSERT HERE>
>-->
>
>My Question:  Is there any way to just selectively take this text
>file, delete <INSERT HERE> and then rewrite the file to a different
>name WITHOUT loading the ENTIRE file into memory and REWRITING the
>whole thing....?
>
>Ie, I need to search in the text file for somthing (even though I
>ALWAYs know where the thing I am looking for is), then remove that
>word, replace it with another, and then rewrite the file.
>
>Can I do it, or do I have to load the entire file into memory and
>then work with string handlers from there before rewriting.

Marc, you really need to specify the Pascal you're using, which
release it is (e.g., Turbo Pascal 5.5), and whether you have the
manuals. (Your other recent postings, re reading Ctrl and Alt chars
and executing an external program, fall clearly into the RTFineM
category.)

_If_ you are using Turbo Pascal (at least for MS-DOS), given that you
know the location and length of the placeholder string
("<INSERT HERE>"), you can simply:

        open in and out files as untyped files of "record size" 1

        BlockRead the in file, BlockWrite the out file to the byte
        immediately before the placeholder

        BlockWrite the outfile with the value to be inserted

        Seek behond the placeholder in the in file

        BlockRead the remainder of the in file and BlockWrite it to
        the out file.

        close the files

Performance will depend largely on the size of the buffer you use
for the BlockReads. If you can use a buffer at least as large as the
larger portion of the in file, you should be able to do this entire
procedure rapidly (relative to the size of the file).

Be sure to RTFineM regarding return values from BlockRead and
BlockWrite.

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| Karl Brendel                           Centers for Disease Control |
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