int variable with leading zero?

Question

Why is it that following results in 34? It doesn't seem to have anything to do with octal numbers.

intval(042);

Answer 1

It does have to do with octal numbers, 042 is interpreted as the octal number 42 which is 4 * 8 + 2 = 34.

Please be aware that the octal interpretation happens when the number literal is parsed while loading the PHP script. It has nothing to do with intval(), which doesn't do anything here because the value is already integer.

Octal interpretation happens only with number literals, not when casting a string to integer:

intval(042)   // == 34
intval('042') // == 42
(int)'042'    // == 42

Answer 2

but a leading 0 does indicate octal in many languages, as is the case here.