Can I somehow know which replacement is taking place from within a callback of preg_replace_callback?

问题

I'm using preg_replace_callback to substitute particular tokens within the string. But apart from actual token I need to know as well whether that token was first, second or third in a subject string. Is there any way to access that info?

I found an argument $count in preg_replace_callback definition (http://php.net/manual/en/function.preg-replace-callback.php), which counts replacements, but I'm not sure if it is accessible from within callback. Any example of the usage in described context?

回答1:

The $count out variable is only set after all the replacements are done. Instead, try a static variable:

function repl($matches) {
    static $count = 0;
    ++$count;
    ...
}
preg_replace_callback('/.../', 'repl', $haystack);

回答2:

You can always create a non-local variable to keep the count.

回答3:

With php 5.3+ you can also use a closure (instead of a global or static variable)

$counter = 0
preg_replace_callback('/.../', function($matches) use(&$counter) {
  ++$counter;
  ...
  },  $haystack
);

来源：https://stackoverflow.com/questions/2482493/can-i-somehow-know-which-replacement-is-taking-place-from-within-a-callback-of-p