New line to paragraph function

I have this interesting function that I'm using to create new lines into paragraphs. I'm using it instead of the nl2br() function, as it outputs better formatted text.

function nl2p($string, $line_breaks = true, $xml = true) {

$string = str_replace(array('<p>', '</p>', '<br>', '<br />'), '', $string);

// It is conceivable that people might still want single line-breaks
// without breaking into a new paragraph.
if ($line_breaks == true)
    return '<p>'.preg_replace(array("/([\n]{2,})/i", "/([^>])\n([^<])/i"), array("</p>\n<p>", '<br'.($xml开发者_运维百科 == true ? ' /' : '').'>'), trim($string)).'</p>';
else 
    return '<p>'.preg_replace(
    array("/([\n]{2,})/i", "/([\r\n]{3,})/i","/([^>])\n([^<])/i"),
    array("</p>\n<p>", "</p>\n<p>", '<br'.($xml == true ? ' /' : '').'>'),

    trim($string)).'</p>'; 

}

The problem is that whenever I try to create a single line break, it inadvertently removes the first character of the paragraph below it. I'm not familiar enough with regex to understand what is causing the problem.

Here is another approach that doesn't use regular expressions. Note, this function will remove any single line-breaks.

function nl2p($string)
{
    $paragraphs = '';

    foreach (explode("\n", $string) as $line) {
        if (trim($line)) {
            $paragraphs .= '<p>' . $line . '</p>';
        }
    }

    return $paragraphs;
}

If you only need to do this once in your app and don't want to create a function, it can easily be done inline:

<?php foreach (explode("\n", $string) as $line): ?>
    <?php if (trim($line)): ?>
        <p><?=$line?></p>
    <?php endif ?>
<?php endforeach ?>

The problem is with your match for single line breaks. It matches the last character before the line break and the first after. Then you replace the match with <br>, so you lose those characters as well. You need to keep them in the replacement.

Try this:

function nl2p($string, $line_breaks = true, $xml = true) {

$string = str_replace(array('<p>', '</p>', '<br>', '<br />'), '', $string);

// It is conceivable that people might still want single line-breaks
// without breaking into a new paragraph.
if ($line_breaks == true)
    return '<p>'.preg_replace(array("/([\n]{2,})/i", "/([^>])\n([^<])/i"), array("</p>\n<p>", '$1<br'.($xml == true ? ' /' : '').'>$2'), trim($string)).'</p>';
else 
    return '<p>'.preg_replace(
    array("/([\n]{2,})/i", "/([\r\n]{3,})/i","/([^>])\n([^<])/i"),
    array("</p>\n<p>", "</p>\n<p>", '$1<br'.($xml == true ? ' /' : '').'>$2'),

    trim($string)).'</p>'; 
}

I also wrote a very simple version:

function nl2p($text)
{
    return '<p>' . str_replace(['\r\n', '\r', '\n'], '</p><p>', $text) . '</p>';
}

@Laurent's answer wasn't working for me - the else statement was doing what the $line_breaks == true statement should have been doing, and it was making multiple line breaks into <br> tags, which PHP's native nl2br() already does.

Here's what I managed to get working with the expected behavior:

function nl2p( $string, $line_breaks = true, $xml = true ) {

    // Remove current tags to avoid double-wrapping.
    $string = str_replace( array( '<p>', '</p>', '<br>', '<br />' ), '', $string );

    // Default: Use <br> for single line breaks, <p> for multiple line breaks.
    if ( $line_breaks == true ) {
        $string = '<p>' . preg_replace(
            array( "/([\n]{2,})/i", "/([\r\n]{3,})/i", "/([^>])\n([^<])/i" ),
            array( "</p>\n<p>", "</p>\n<p>", '$1<br' . ( $xml == true ? ' /' : '' ) . '>$2' ),
            trim( $string ) ) . '</p>';

    // Use <p> for all line breaks if $line_breaks is set to false.
    } else {
        $string = '<p>' . preg_replace(
            array( "/([\n]{1,})/i", "/([\r]{1,})/i" ),
            "</p>\n<p>",
            trim( $string ) ) . '</p>';
    }

    // Remove empty paragraph tags.
    $string = str_replace( '<p></p>', '', $string );

    // Return string.
    return $string;

}

Here's an approach that comes with a reverse method to replace paragraphs back to regular line breaks and vice versa.

These are useful to use when building a form input. When saving a users input you may want to convert line breaks to paragraph tags, however when editing the text in a form, you may not want the user to see any html characters. Then we would replace the paragraphs back to line breaks.

// This function will convert newlines to HTML paragraphs
// without paying attention to HTML tags. Feed it a raw string and it will
// simply return that string sectioned into HTML paragraphs
function nl2p($str) {
    $arr=explode("\n",$str);
    $out='';

    for($i=0;$i<count($arr);$i++) {
        if(strlen(trim($arr[$i]))>0)
            $out.='<p>'.trim($arr[$i]).'</p>';
    }
    return $out;
}

// Return paragraph tags back to line breaks
function p2nl($str)
{
    $str = preg_replace("/<p[^>]*?>/", "", $str);
    $str = str_replace("</p>", "\r\n", $str);
    return $str;
}

Expanding upon @NaturalBornCamper's solution:

function nl2p( $text, $class = '' ) {
    $string = str_replace( array( "\r\n\r\n", "\n\n" ), '</p><p>', $text);
    $string = str_replace( array( "\r\n", "\n" ), '<br />', $string);
    return '<p' . ( $class ? ' class="' . $class . '"' : '' ) . '>' . $string . '</p>';
}

This takes care of both double line breaks by converting them to paragraphs, and single line breaks by converting them to <br />

Just type this between your lines:

echo '<br>';

This will give you a new line.