Execute a function on each element of an array

Question

I am aware of array_walk() and array_map(). However when using the former like so (on an old project) it failed

array_walk($_POST, 'mysql_real_escape_string');

Warning: mysql_real_escape_string() expects parameter 2 to be resource, string given.

So I went with this slightly more ugly version

foreach($_POST as $key => $value) {
    $_POST[$key] = mysql_real_escape_string($value);
}

So why didn't the first way work? What is the best way to map values of an array to a function?

Answer 1

The callback function passed to array_walk is expected to accept two parameters, one for the value and one for the key:

Typically, funcname takes on two parameters. The array parameter's value being the first, and the key/index second.

But mysql_real_escape_string expects the second parameter to be a resource. That’s why you’re getting that error.

Use array_map instead, it only takes the value of each item and passes it to the given callback function:

array_map('mysql_real_escape_string', $_POST);

The second parameter will be omitted and so the last opened connection is used.

If you need to pass the second parameter, you need to wrap the function call in another function, e.g. an anonymous function:

array_map(function($string) use ($link) { return mysql_real_escape_string($string, $link); }, $_POST);