array_walk_recursive, function using variable outside in PHP

Question

   $total_materials_cost = 0;
   array_walk_recursive($materials, function($item, $key) {
        if (in_array($key, array('id'))) {

                    (....)

                    $total = $material_price * $material['amount'];

                    $total_materials_cost += $total;
                }
            }
        }
    });
echo $total_materials_cost;

For the above code I get error at line $total_materials_cost += $total; , says the variable is undefined - I believe this is because that I am inside a function? But how can I in any way bypass/ make a workaround for this, so it does add to the variable?

I find it VERY unlikely that you need a recursive approach. It is more likely, if needing any special iterating at all, that you just need nested loops. If the subarrays have consistent depth, using recursion is needless overhead and `array_walk_recursive()` will unnecessarily visiting every leafnode. This old question really would have benefited from sample input. Also, `in_array()` is another needless overhead. — mickmackusa, Dec 03 '19 at 10:07

knittl · Accepted Answer · 2012-09-02T19:02:36.320

17

Use the use keyword:

$total_materials_cost = 0;
array_walk_recursive($materials, function($item, $key) use(&$total_materials_cost) {
  if (in_array($key, array('id'))) {
    // (....)
    $total = $material_price * $material['amount'];
    $total_materials_cost += $total;
  }
});
echo $total_materials_cost;

Pass a reference (&) to change a variable outside the closure.

edited Sep 02 '12 at 19:02

answered Sep 02 '12 at 18:53

knittl

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error gone but $total_materials_cost is 0 and does not add – Karem Sep 02 '12 at 18:58
@Karem: Sorry, missed that. Please see my updated answer. – knittl Sep 02 '12 at 19:02

array_walk_recursive, function using variable outside in PHP

1 Answers1