Question

In PHP, you can access characters in a string with the array syntax:

$foo = 'abc';
echo $foo[2]; // echos 'c'

I recently spent way too long debugging why $foo['id'] wasn’t giving me the expected result. It turned out that $foo was a string instead of an associative array. PHP seemed to be casting 'id' to the integer 0, without giving any notice:

$foo = 'abc';
echo $foo['id']; // echos 'a', without notice

PHP throws a nice warning when you do this with real arrays:

$foo = array('a', 'b', 'c');
$echo $foo['id']; // Notice:  Undefined index: id in php shell code on line 1

How can I make (or why can’t) PHP throw an “Undefined index” notice instead of casting a string index to 0?

Answer 1

Unfortunately, there’s nothing you can do, short of patching PHP.

However, if you do want to patch PHP, this is a possible patch (against trunk):

Index: Zend/zend_execute.c
===================================================================
--- Zend/zend_execute.c (revision 316974)
+++ Zend/zend_execute.c (working copy)
@@ -1268,7 +1268,7 @@
                                                case IS_DOUBLE:
                                                case IS_NULL:
                                                case IS_BOOL:
-                                                       /* do nothing */
+                                                       zend_error(E_NOTICE, "String offset is not an integer");
                                                        break;
                                                default:
                                                        zend_error(E_WARNING, "Illegal offset type");

Then:

$ ~/php/php-t/bin/php -d error_reporting=-1 -r '$a="foo"; echo $a["bar"];'

Notice: String offset is not an integer in Command line code on line 1
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