-The second 'feature' is that although constants are case sensitive (by -default), you cannot declare a constant twice with alternative -cases. E.g., -
- --%module example - -#define TEST Hello -#define Test World --
-accessed from PHP, -
- -
-include("example.php");
-
-echo TEST, Test;
-
--will output "Hello Test" rather than "Hello World". This is because -internally, all constants are stored in a hash table by their lower -case name, so 'TEST' and 'Test' will map to the same hash element -('Test'). But, because we declared them case sensitive, the Zend -engine will test if the case matches with the case the constant was -declared with first. -
- --So, in the example above, the TEST constant was declared first, and -will be stored under the hash element 'test'. The 'Test' constant will -also map to the same hash element 'test', but will not overwrite -it. When called from the script, the TEST constant will again be -mapped to the hash element 'test' so the constant will be -retrieved. The case will then be checked, and will match up, so the -value ('Hello') will be returned. When 'Test' is evaluated, it will -also map to the same hash element 'test'. The same constant will be -retrieved, this time though the case check will fail as 'Test' != -'TEST'. So PHP will assume that Test is a undeclared constant, and as -explained above, will return it as a string set to the constant name -('Test'). Hence the script above will print 'Hello Test'. If they were -declared non-case sensitive, the output would be 'Hello Hello', as -both point to the same value, without the case test taking place. ( -Apologies, this paragraph needs rewriting to make some sense. ) -
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