The PHP keyword replaces only once the implementation function _php technique

There's nothing to say about replacing a keyword with a bulk replacement, but what you need here is that each keyword needs to be replaced only once. Check the PHP related function document, found that PHP itself is not a function to achieve this function, so have to solve their own. summed up several feasible methods, small remember!
(1) using the Preg_replace function to implement this function, because the Preg_replace function itself can be implemented to control the number of replacements, so the first thought of him, the specific implementation of the following methods:

Can be implemented to control the number of substitutions, not only to replace only once, such as $limit 2 when a word appears a lot of eating only 2 times,-1 to replace all. $search and $replace can be either strings or arrays, but must correspond to 
function Str_replace_limit ($search, $replace, $content, $limit =-1) { 
  if ( Is_array ($search)) { 
    foreach ($search as $k => $v) { 
      $search [$k]=]. Preg_quote ($search [$k], ""). ' `'; 
    } 
  } else{ 
    $search = '. Preg_quote ($search, '). `'; 
  } 
  Remove the picture description 
  $content =preg_replace ("/alt= ([^ >]+)/is", $content); 
  Return Preg_replace ($search, $replace, $content, $limit); 
 

(2) using the Substr_replace function, but only one replacement can be implemented here

First find the location of the keyword and then use Substr_replace (System function) to replace the operation 
function Str_replace_once ($search, $replace, $content) { 
  // Remove the picture description 
  $content =preg_replace ("/alt= ([^ >]+)/is", $content); 
  $pos =strpos ($content, $search); 
  if ($pos ===false) {return 
    $haystack; 
  } 
  Return Substr_replace ($content, $replace, $pos, strlen ($search)); 

' Above is the PHP only replaces once and controls the replacement number The realization function, hoped that has the help to everybody's study.