Question

I’m facing a weird issue with PHP. This simple example:

<?php
$array = array(
  'zero',
  'one',
  'id' => 'two'
);

foreach ($array as $key => $value) {
  if ($key == "id") {
    echo "Key: ". $key .", value: ". $value ."\n";
  }
}
?>

should (imho) output this:

Key: id, value: two

But it outputs

Key: 0, value: zero
Key: id, value: two

How is this possible: 0 == "id"?

Answer 1

When $key is 0 and gets compared to the string “id“, the string (“id“) will be converted to an integer. Since “id” can’t be turned into a valid integer that conversion will yield 0, and the if statement becomes true.

Since you don’t want the implicit conversion to happen between two types who aren’t compatible use the more strict === version of ==. === will see if the variables are of the same type and has the same exact value.

 if ($key === "id") {
   ...
 }

Documentation PHP: Comparison Operators

---

Examples

var_dump (0         == (int)"id");
var_dump ((string)0 == "id");
var_dump (0        === "id");

var_dump (1.0 === 1);

output

bool(true)
bool(false)
bool(false)
bool(false) # be careful!