EC
UnderflowException
PHPERRORCommonBounds

Removing from an empty container

Quick Answer

Check isEmpty() before pop/dequeue; throw UnderflowException to signal an empty container.

What this means

Thrown when an element is removed from or requested on an empty container.

Why it happens
  1. 1Popping from an empty stack
  2. 2Dequeuing from an empty queue

Fix

Check before removal

Check before removal
public function pop(): mixed {
    if (empty($this->items)) {
        throw new \UnderflowException("Cannot pop from an empty stack");
    }
    return array_pop($this->items);
}

Why this works

Explicit empty check prevents undefined behavior and provides a clear error message.

Code examples
SplStack popphp
$s = new \SplStack();
$s->pop(); // RuntimeException: Can't pop from an empty datastructure
Custom guardphp
if ($stack->isEmpty()) {
    throw new \UnderflowException("Stack is empty");
}
$val = $stack->pop();

Content generated with AI assistance and reviewed for accuracy. Found an error? hello@errcodes.dev

← All PHP errors