php array behaving strangely with key value 07 & 08

Question

I have an array for months

$months[01] = 'January';
$months[02] = 'February';
$months[03] = 'March';
$months[04] = 'April';
$months[05] = 'May';
$months[06] = 'June';
$months[07] = 'July';
$months[08] = 'August';
$months[09] = 'September';
$months[10] = 'October';
$months[11] = 'November';
$months[12] = 'December';

Now the array does not output correct value for key 07 & 08.

Try doing print_r($months) you will not get any key value August and zero key index for September.

Though I’m able to solve the problem by removing the leading zero, still I would love to know the reason for same.

Even the PHP editor spots some problem but unable to tell what is the problem.

Thanks

The worst about how PHP handles this is not that it lets you accidentally use octal when you didn't intend to, but that it evaluates 08 and 09 as 0 silently, which confuses people not aware of octal even more, producing this seemingly random behavior of eating up the value assigned to [08] and associating the value assigned to [09] actually to [0]. PHP's choice to partially parse numbers and when it finds a token stopper just ignores the rest (as does in this example and also when casting a string to an int) is a really bad choice. — Petruza
– Petruza, Commented Apr 2, 2019 at 13:12

Emil H · Accepted Answer · 2011-01-20 18:13:19Z

11

Prepending 0 before a number means PHP parses it as an octal value in the same way that prepending 0x causes it to be parsed as a hexadecimal value. Remove the zero, and it will work fine.

echo 07; // prints 7
echo 010; // prints 8

This is mostly used when specifying unix permissions:

chmod("myfile", 0660);

Except for that it's rarely something that you'd want to do.

This is described in the PHP Manual.

edited Jan 20, 2011 at 18:13

answered Jan 20, 2011 at 18:06

Emil H

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Comments

Sam Dufel · Accepted Answer · 2011-01-20 18:07:42Z

4

Generally, putting a leading 0 on a number tells the compiler that you've giving an octal number (base 8, not base 10).

In octal, 8 and 9 don't exist (8 is 010, 9 is 011), so you're confusing php.

If you really want a leading zero, you can use strings for your indexes

answered Jan 20, 2011 at 18:07

Sam Dufel

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Mike Valstar · Accepted Answer · 2011-01-20 18:07:58Z

3

PHP will treat numbers with a leading 0 as octal numbers, either drop the leading 0 or put the key values in quotes.

answered Jan 20, 2011 at 18:07

Mike Valstar

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Peter Bailey · Accepted Answer · 2011-01-20 18:11:08Z

3

The way you form an integer literal is important.

See the structure for decimal literals? Notice how a preceeding zero is not part of that pattern?

Either you have to remove the zeros, or treat your array keys as strings

$months['01'] = 'January';
$months['02'] = 'February';
// etc...

answered Jan 20, 2011 at 18:11

Peter Bailey

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Petruza · Accepted Answer · 2011-08-04 18:06:15Z

0

I just realized this after precious minutes of debugging and table head banging.
The problem is that PHP doesn't raise an error or even a warning about having malformed the octal literal integer. It just ignores the part from the error until the end of the literal.
Damn.

PS: Who uses octal numbers? never did, never heard of someone using them for a good reason.
Hexadecimal is great, but octal? damn.
Even for permission I usually do chmod ugo+rwx is more straightforward.

answered Aug 4, 2011 at 18:06

Petruza

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