PHP函数nl2br()与自定义函数nl2p()换行用法分析

<?php
$str = "Welcome to 
www.jb51.net";
echo nl2br($str);
?>

Welcome to <br />
www.jb51.net

<?php
function nl2p($text) {
 return "<p>" . str_replace("\n", "</p><p>", $text) . "</p>";
}
?>

/**
 * Returns string with newline formatting converted into HTML paragraphs.
 *
 * @param string $string String to be formatted.
 * @param boolean $line_breaks When true, single-line line-breaks will be converted to HTML break tags.
 * @param boolean $xml When true, an XML self-closing tag will be applied to break tags (<br />).
 * @return string
 */
function nl2p($string, $line_breaks = true, $xml = true)
{
  // Remove existing HTML formatting to avoid double-wrapping things
  $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'.($xml == true ? ' /' : '').'>'), trim($string)).'</p>';
  else 
    return '<p>'.preg_replace("/([\n]{1,})/i", "</p>\n<p>", trim($string)).'</p>';
}