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-   -   Need help with a little algorithm thing. (http://www.programmingforums.org/showthread.php?t=12149)

Intimidat0r Dec 10th, 2006 2:35 AM
Need help with a little algorithm thing.
 
Well, here's my dilemma. I'm kind of new to PHP, although I've done a lot of simple stuff with it.

I'm trying to go through a string, let's call it $str, and replace every occurrence of a newline (\n) with "<p />".

However (and this is what makes it difficult) I don't want to perform the replacement if the \n falls between <pre> and </pre> tags.

I've tried to accomplish this with a bit of looping, but to no avail. Can anyone here help me on this?

Thanks a bunch guys. :D

grimpirate Dec 10th, 2006 3:32 AM
For replacement you can use the function str_replace()
For instance:
str_replace ("\n", "<p />", $str);
The other half is slightly more tricky as there are lots of ways of doing it. I'll show one later, it's late *_*

Jimbo Dec 10th, 2006 4:17 AM
not-so-pseudo-code, no guarantees as to correctness
:
$insidePre = false;
for($i = 0; i < strlen($theString); $i++)
{
  if(!$insidePre && $theString[$i] == '\n')
    $theString = substring($theString, 0, i) . "<p />" . substring($theString, i+1);
  else if(!$insidePre && substring($theString, i, 5) == "<pre ")
    $insidePre = true;
  else if($insidePre && substring($theString, i, 6) == "</pre ")
    $insidePre = false;
}
Like I said, no guarantees....

DaWei Dec 10th, 2006 5:53 AM
Another similar approach I've used is to take the text as one huge string and break it into lines. You can then use the pre tags to indicate those sections in which you replace newlines (or crlf, or whatever your format has) with <p/> (they're all at the end of the line, of course). When I used it, I actually substituted <p>s and </p>s at the appropriate points. You'll note that except for the beginning and end, and inside <pre> tags, the paragraph breaks come as a </p><p> pair.

Intimidat0r Dec 10th, 2006 2:52 PM
Jimbo: Yeah, I was having a bit of trouble getting that to work. I changed yours around a bit, but to no avail.

:
function format($theString)
{
 $insidePre = false;
 for($i = 0; $i < strlen($theString); $i++)
 {
  if(!$insidePre && substr($theString, $i, 1) == "\n")
  $theString = substr($theString, 0, $i)."<p />".substr($theString,$i+1);
  else if(!$insidePre && substr($theString, $i, 5) == "<pre ")
  $insidePre = true;
  else if($insidePre && substr($theString, $i, 6) == "</pre>")
  $insidePre = false;
 }
 return $theString;
}

DaWei: I'm afraid I don't quite understand.

a thing Dec 10th, 2006 3:04 PM
You should be using <br/> instead of an empty <p>.

Intimidat0r Dec 10th, 2006 3:14 PM
Unfortunately using <br /> screws up the tables, so I have to use <p />

Jimbo Dec 10th, 2006 8:05 PM
Try this and see how it works. I did a quick test and I think it was working properly:
:
function format($theString)
{
  $insidePre = false;
  for($i = 0; $i < strlen($theString); $i++)
  {
    if(!$insidePre && substr($theString, $i, 1) == "\n")
      $theString = substr($theString, 0, $i)."<p />".substr($theString,$i+1);
    else if(!$insidePre && (substr($theString, $i, 5) == "<pre>" ||
          substr($theString, $i, 5) == "<pre "))
      $insidePre = true;
    else if($insidePre && substr($theString, $i, 6) == "</pre>")
      $insidePre = false;
  }
  return $theString;
}

And, as DaWei mentioned, you might consider changing the logic to pair the tags properly. If you do, you'll need a little extra logic for closing the last tag but not opening a new one.

Intimidat0r Dec 11th, 2006 1:25 AM
Thanks guys. That worked beautifully Jimbo. :)

<3

headzoo Dec 13th, 2006 2:58 AM
Quote:
Originally Posted by Intimidat0r (Post 120961)
I'm trying to go through a string, let's call it $str, and replace every occurrence of a newline (\n) with "<p />".

However (and this is what makes it difficult) I don't want to perform the replacement if the \n falls between <pre> and </pre> tags.
I think I'm a bit late to the party here, since Intimidat0r's question has already been answered. But I can't help wondering why a regular expression isn't being used? This is exactly the type of thing that regexp were designed for.

Forget all the looping and complicated stuff. There is a 1 line solution:

:
echo preg_replace('/(?!((<pre.*?)))\n(?!(([^>]*?<\/pre>)))/', '<p/>', $str);

This will replace all occurrences of \n of <p/>, but not if the \n falls in between a pair of <pre></pre> tags.

- Sean


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