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From: "Steve" <nospam_steved94@comcast.net>
Newsgroups: comp.lang.ada
References: <l22pt2114r910becfeg00e1dl1vb7flesq@4ax.com>
Subject: Re: Text Processing in Ada 95
Date: Thu, 22 Feb 2007 20:55:30 -0800
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Date: 2007-02-22T20:55:30-08:00
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"Rob Norris" <firstname.lastname@baesystems.com> wrote in message 
news:l22pt2114r910becfeg00e1dl1vb7flesq@4ax.com...
>
> Suppose I have a text file such as:
>
> tom
> dick
> harry
>
> Then I want to insert the line "dave" after tom so the file is
>
> tom
> dave
> dick
> harry
>
> Also suppose text file can get rather large.
>
> Currently I'm using text_io which means I have to copy the whole thing 
> into memory, insert the line
> then over write the file with new contents. direct_io is not an option 
> (varing string lengths)

Actually Direct_IO is an option, and probably the fastest way to handle the 
operation.

  Step 1. Determine the initial file size
  Step 2. Allocate a buffer that is the size of the file plus the size of 
the string you want to add (including a line terminator)
  Step 3. Create an instance Direct_IO that is the file size
  Step 5. Read the file into the start of the allocated buffer in one gulp
  Step 6. Insert your string in the buffer (a little tricky, but doable)
  Step 7. Create an instance of Direct_IO that is the size of the buffer 
with the new string
  Step 8. Write the buffer to a file as one operation.

It's kind of messy to deal with the content of a text file in a buffer, and 
will not work on systems with structured files (like VMS) but will work on 
most modern systems.

Regards,
Steve
(The Duck)

>
> What alternatives should I consider for making insertions faster?
> (NB retrieval of a line needs to be fairly quick as well).
>
> Thanks in advance.