$a = 'a';
echo isset($a['b']);
This code returns 1. Why?
5 Answers
String characters can be referenced by their offset using syntax like $a[0] for the first character, e.g.
$string = 'Hello';
echo $string[1]; // echoes 'e'
so PHP is recognising that $a is a string; casting your 'b' to a numeric (which casts to a 0), and trying to test isset on $a[0], which is the first character a
Though it should also throw an illegal offset 'b' warning if you have errors enabled
EDIT
$a = 'a';
echo isset($a['b']), PHP_EOL;
echo $a['b'];
PHP 5.3
1
a
PHP 5.4
Warning: Illegal string offset 'b' in /Projects/test/a10.php on line 6
a
PHP 5.5
PHP Warning: Illegal string offset 'b' in /Projects/test/a10.php on line 6
Warning: Illegal string offset 'b' in /Projects/test/a10.php on line 6
a
2 Comments
bansi
@Mark
isset wont throw a warning. and as of php 5.4 Checking non-numeric offsets of strings now returns FALSE.`bansi
strange, I tested it on PHP 5.4.16 (both windows and linux) no warnings for
echo isset($a['b']), just returns false. my error_reporting is set to -1 and display errors is on.Only for php 5.3:
so lets do it slowly:
$a['b'];
returns 'a' because b is converted to 0 and $a[0] (the first char of 0 = a)
isset($a['b']);
return true because $a['b'] is 'a' not null
echo true;
outputs "1" because true is converted to a string and this to "1".
3 Comments
Eddie
Thanks for an explaination. I didn't expect that 'b' will be converted to integer.
bansi
@Christoph you are totally wrong!
isset($a['b']); returns false not true. Have you tested it before posting your answer?
Christoph Diegelmann
@bansi I'm totally right did you test it before posting your comment? I did. (php 5.3.23) Ahh see Mark Baker's answer .. it doesn't work starting with php 5.4
because ISSET return the 1 if the value is set.
Use it like this :
if(isset($a['b']){
echo $a['b'];
}
<?php
$a = 'a';
var_dump($a);
?>
it will gives output string(1) "a"
if you will echo $a['b'] it will give you output as a so $a['b'] also has value
hence
<?php
$a = 'a';
echo isset($a['b']);
?>
outputs value 1
echo isset($a);returns 1.isset($a['b'])returns false.