PHP and leading zeroes mindtrick

[cenobite321]

Hello everyone,

I've just got an e-mail from a friend telling me how PHP disliked leading zeroes. He attached the following code:

 <?php
 for($i=01;$i<=07;$i++){
 print $i;
 echo "<br>";
 }
 
 for($i=01;$i<=08;$i++){//with 8 or more it fails
 print $i;
 echo "<br>";
 }
 ?>

As the comment highlights the second for statement fails and numbers are not displayed like in the first one. I made the following analysis of both numbers:

 $foo = 07;
 //print the type of 07
 print '07 is a: '.gettype($foo).'<br>';
 //print the value of 07
 print $foo.'<br>';
 //adds 07 plus 1 and prints the result
 $foo = $foo +1;
 print $foo.'<br>';
 
 
 $foo = 08;
 //print the type of 08
 print '08 is a: '.gettype($foo).'<br>';
 //print the value of 08
 print $foo.'<br>';
 //adds 08 plus 1 and prints the result
 $foo = $foo +1;
 print $foo.'<br>';

The outcome was this:

07 is a: integer
7
8
08 is a: integer
0
1

Weird...:nuts:

 

[marshian]

PHP doesn't dislike leading zeroes, leading zeroes mean something =P

I have a test for you, try the following script before you read on:

<?php
header("Content-type: text/plain");

$one = 001;
$eight = 010;
echo $one * $eight;
?>

Do you know now?

-----------------------
A leading zero means the number is octal. The octal numeric system consists of 8 different numbers (0-7), it's related to the hexadecimal system, which uses 16 (0-F).
If you write 01, this means 1⁽⁸⁾ (read: 1 the numeric system with 8 symbols). This also equals 1⁽¹⁰⁾ in the more common decimal system.
Writing 010 however means 10⁽⁸⁾ which is the same as 8⁽¹⁰⁾.
Thus, using 8 or 9 in a number with leading zero indicates an invalid number (since 8 and 9 don't exist in the octal system). Therefore, the variable is assigned the default value of 0.
That pretty much explains this phenomenon, any questions?

 

[descalzo]

Weird...:nuts:

Not really.

In most programming languages

x = 011

gives x the value of 9.

while

y = 0x11

gives y the value of 17

Leading 0x signifies hexidecimal, or base 16. You use 0-9 and a-f (or A-F) as numerals.
Leading 0 with no x signifies octal, or base 8. You use 0-7 as numerals.

Since 8 is not a legal octal numeral, 08 either causes an error, or is evaluated as zero ( 0118 would be evaluated as 011 or decimal 9).

 

[misson]

For reference, this is documented on the PHP Integers manual page.