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Re: Re: Re: Re: Efficienty truncating a long string

by ysth (Canon)
on Dec 18, 2003 at 10:03 UTC ( [id://315480]=note: print w/replies, xml ) Need Help??

in reply to Re: Re: Re: Efficienty truncating a long string
in thread Efficienty truncating a long string

4-arg substr isn't optimized for void context. It will set up the replaced string to be returned regardless.

The lvalue substr doesn't actually return the string but a special lvalue indicating the offset and length. Creating this and setting it to '' involves a fair amount of overhead.

Which is actually more efficient will probably depend on how much you are truncating.

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Re: Efficienty truncating a long string
by dino (Sexton) on Dec 18, 2003 at 10:28 UTC
    It was originally part of a log reader. I found that reading in blocks and working pattern matching on those blocks was much more efficient than on line by line. Obviously you can get partial lines, so I rindex the last /n, save the fragment at the end for the next pass and return the main block truncated. It works like a charm. I was reinventing it and seing how I could make it more efficient.
      Then you probably want to use 4-arg substr to truncate the buffer and save the fragment all at once:
      $end = rindex($buffer, "\n"); if ($end < 0) { whoops, incomplete line } $fragment = substr($buffer, $end+1, length($buffer), '');
      Note that length($buffer) is bigger than the actual length(buffer)-$end-1 you want, but specifying a length larger than is available is guaranteed to not cause problems; you'll just get what is there. If the buffer ends with "\n", you'll get an empty $fragment.

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