By opening a file you get a cursor into it. It’s the thing you move with seek.

When you read, say, 20 bytes from the file, the cursor moves forward 20 bytes, so the next read will return the next part.

When you write, say, 20 bytes to the file, the cursor moves forward 20 bytes, so the next write will write the next part. If the there was already something past where the cursor was pointing, and you write 20 bytes at that position, then 20 bytes of previous content get overwritten.

That much should be pretty clear; according to what you say, you already understand that.

Now, there’s no reason you need to always write or always read. You can read 20 bytes, then write 20 bytes; the cursor will now be before the 40th byte, waiting for your next action. Or you can seek around wildly, reading here, writing there, doing whatever wherever.

That’s all there is to it.

Still confused?

Makeshifts last the longest.

In reply to Re: Using +> for File Read/Write by Aristotle
in thread Using +> for File Read/Write by slloyd

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.