PHP Secrets: Weird Coding Tricks & Hidden Bugs

Explore the weirdest PHP tricks, hidden bugs, and debugging secrets every developer should know. From type juggling to loose comparison bugs, learn how to write cleaner, safer, and more secure PHP code. This guide reveals PHP pitfalls with demos, corrections, and expert tips to protect your apps. Perfect for beginners and pros alike. Boost your code confidence and avoid common traps today.

PHP secrets, weird coding tricks, and hidden bugs that can surprise even experienced developers. These quirks often arise from PHP’s loose type juggling, legacy behavior, and design choices. Be careful—some of them are dangerous in production!

1. ‘0e1234’ == ‘0’ returns true (Type Juggling Gotcha)

Why?

PHP converts both strings to floats. '0e1234' is scientific notation and becomes 0.0. So '0e1234' == '0' is true.

Demo:

var_dump('0e1234' == '0'); // true

Correction:

var_dump('0e1234' === '0'); // false

Tip:

Always use === for comparing user credentials like hashed passwords.

2. ‘php’ == 0 returns true

Why?

Non-numeric strings become 0 in loose comparisons.

Demo:

var_dump('php' == 0);

Correction:

var_dump('php' === 0); // false

Tip:

Don’t mix types. Avoid == between strings and numbers.

3. ‘0’ is falsy but ‘false’ is truthy

Why?

Only '0' is treated as falsy among non-empty strings.

Demo:

if ('0') echo 'Truthy'; else echo 'Falsy'; // Falsy
if ('false') echo 'Truthy'; else echo 'Falsy'; // Truthy

Correction:

Cast explicitly or check using ===.

Tip:

Beware when using user inputs like '0' in conditionals.

4. Leading Zeroes = Octal Confusion

Why?

Numbers starting with 0 are interpreted as octal (base 8).

Demo:

var_dump(010); // int(8)

Correction:

var_dump(10); // int(10)

Tip:

Don’t prefix integers with 0 unless intentional.

5. Loose comparisons with booleans

Why?

PHP coerces types for ==. 'false' == false → 'false' becomes 0, false becomes 0, so it’s true.

Demo:

var_dump('false' == false); // true

Correction:

var_dump('false' === false); // false

Tip:

Always use strict comparisons.

6. Array keys get overwritten silently

Why?

PHP converts true, 1, '1' all to the same key: 1.

Demo:

$arr = [true => 'a', 1 => 'b', '1' => 'c'];
print_r($arr); // [1 => 'c']

Correction:

Use distinct string keys.

Tip:

Avoid using booleans or ambiguous values as array keys.

7. Negative string offsets (PHP 7.1+)

Why?

PHP 7.1 added support for negative string indexing.

Demo:

echo 'hello'[-1]; // o

Correction:

Validate length first for compatibility.

Tip:

Great for getting the last character in PHP 7.1+.

8. Floating Point Math Precision

Why?

Binary representation can’t perfectly represent decimal fractions.

Demo:

var_dump((0.1 + 0.7) * 10 == 8); // false

Correction:

var_dump(round((0.1 + 0.7) * 10) == 8); // true

Tip:

Use round(), bcadd() or bcmath functions for money.

9. foreach Affects Array Pointer

Why?

foreach modifies internal pointer (next(), current()).

Demo:

$arr = [1, 2, 3];
foreach ($arr as $v) {}
echo current($arr); // false

Correction:

reset($arr);

Tip:

Use foreach for iteration only.

10. Dangling references in foreach

Why?

Referenced variable retains reference after loop ends.

Demo:

$arr = [1, 2, 3];
foreach ($arr as &$val) {}
foreach ($arr as $val) {}
print_r($arr); // Last element messed up

Correction:

unset($val);

Tip:

Always unset reference variables after foreach (&$item).

11. isset() vs array_key_exists()

Why?

isset() returns false for null values; array_key_exists() checks the key only.

Demo:

$a = ['foo' => null];
var_dump(isset($a['foo'])); // false
var_dump(array_key_exists('foo', $a)); // true

Correction:

Use array_key_exists() when checking key presence.

Tip:

Don’t use isset() to check if a key exists if values can be null.

12. Empty Array + Index Assignment Skips Numeric Indexing

Why?

Directly assigning to a numeric index doesn’t auto-increment.

Demo:

$a = [];
$a[5] = 'PHP';
print_r($a); // [5 => 'PHP']
$a[] = 'Dev';
print_r($a); // [5 => 'PHP', 6 => 'Dev']

Tip: Index starts from highest numeric key + 1 when using $a[].