Common errors

A warning lets the script continue (often with a null value); a fatal error or an uncaught exception stops it. Both name the file and line.

• Warning: Undefined variable $x — a typo, or the variable is from outside a function (pass it in, or use it in a closure).
• Warning: Undefined array key "name" — the key is missing; use $a["name"] ?? null.
• Parse error: syntax error, unexpected … — usually a missing ;, ) or } just before the line shown.
• Fatal error: Uncaught Error: Call to undefined function area() — the file defining it was not required, or the name is misspelled.
• Fatal error: Uncaught TypeError: …must be of type int, string given — an argument does not match the declared type.
• Fatal error: Uncaught DivisionByZeroError — dividing by 0 (PHP 8 throws instead of warning).
• Fatal error: Allowed memory size … exhausted — over the 160 MB limit, often an endless loop that keeps adding to an array.

<?php

$values = ['10', 'x', '7'];
$total = 0;
foreach ($values as $v) {
    if (! is_numeric($v)) {
        echo "skipped $v\n";
        continue;
    }
    $total += (int) $v;
}
echo "total: $total\n";

try {
    echo intdiv(1, 0);
} catch (DivisionByZeroError $e) {
    echo 'caught: ', $e->getMessage(), "\n";
}

skipped x
total: 17
caught: Division by zero