Comparison in Conditions

In an if, PHP does not insist on a real boolean. It converts the value to true or false first. Values that become false are called falsy, and the rest are truthy.

The falsy values

• false
• 0 and 0.0
• "" and "0"
• [] (empty array)
• null

Everything else is truthy, including "false", "0.0", " " (a space) and any non-empty array.

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<?php
$values = [0, 1, "", "0", "hello", [], [0], null, "false"];

foreach ($values as $value) {
    echo json_encode($value) . " is " . ($value ? "truthy" : "falsy") . "\n";
}

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0 is falsy
1 is truthy
"" is falsy
"0" is falsy
"hello" is truthy
[] is falsy
[0] is truthy
null is falsy
"false" is truthy

This is convenient

You can test for “something there” directly.

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<?php
$name = "Mira";

if ($name) {
    echo "Hello, $name";
}

$items = [];

if (!$items) {
    echo "\nYour cart is empty.";
}

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Hello, Mira
Your cart is empty.

And this is a trap

Because 0 and "0" are falsy, a legitimate value can look like “nothing”.

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<?php
$quantity = "0";

if ($quantity) {
    echo "Has a quantity";
} else {
    echo "Treated as empty";
}

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Treated as empty

If 0 is a valid answer (a quantity of zero, an age of zero, a score of zero), write an explicit comparison instead.

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<?php
$quantity = "0";

if ($quantity !== "") {
    echo "A quantity was entered: $quantity";
}

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A quantity was entered: 0

Functions that return false on failure

Many PHP functions return false when they fail, but 0 as a valid answer. Always compare with ===.

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<?php
$position = strpos("PHP", "P");   // 0, a valid position

if ($position !== false) {
    echo "Found at $position";
}

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Found at 0

Which style should you use?

• Use the short form (if ($items)) for “is there anything?” checks on arrays and strings, when zero is not a valid value.
• Use explicit comparisons (=== 0, !== "", === false) whenever zero, an empty string or false could be a real answer.