I think if you want the fastest seek to line on the fly without massive memory overhead, you could go the XS approach. Write a C function somewhat like this -
seek_line(FILE *f, long lineno)
{
  char buffer[65536]; # 64k buffer
  fseek(f, 0, SEEK_SET);
  
  // read in 64 k of text at a time
  fread(buffer, 65536, 1, f);
  
  // then count number of \n's
  
  // if found the desired number of lines, then
  // record the position found, fseek to that
  // position in file, and then return

  // if not enough lines, read next block of 64k text
  // and repeat until you have the desired number of
  // lines. fseek to the absolute position in file
  // for the desired line, and then return
}

[download]
Expose this function in Perl, so that you can do
seek_line($fh, $line_no);
# and then read as normal

[download]

In reply to Re: Re: Re: Fast way to read from file by Roger
in thread Fast way to read from file by Hena

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.