Strange behavior with isset() returning true for an Array Key that does NOT exist

问题

I have the following array called $fruits:

Array
(
    [response] => Array
        (
            [errormessage] => banana
        )  

    [blah] => Array
        (
            [blah1] => blahblah1
            [blah2] => blahblah2
            [blah3] => blahblah3
            [blah4] => blahblah4
        )  

)

Yet when I do:

isset($fruits['response']['errormessage']['orange'])

It returns true!

What on earth would cause such a strange behavior and how can I fix this?

Thanks!

回答1:

[n] is also a way to access characters in a string:

$fruits['response']['errormessage']['orange']
==
$fruits['response']['errormessage'][0] // cast to int
==
b (the first character, at position 0) of 'banana'

Use array_key_exists, possibly in combination with is_array.

回答2:

It just boils down to PHP's crazy type system.

$fruits['response']['errormessage'] is the string 'banana', so you're attempting to access a character in that string by the ['orange'] index.

The string 'orange' is converted to an integer for the purposes of indexing, so it becomes 0, as in $fruits['response']['errormessage'][0]. The 0th index of a string is the first character of the string, so for non-empty strings it's essentially set. Thus isset() returns true.

I don't know what you're trying to do in the first place so I can't offer any "fix" for this. It's by design.

回答3:

to fix

if (is_array($fruits['response']['errormessage']) 
    && isset($fruits['response']['errormessage']['orange'])) { .. }

来源：https://stackoverflow.com/questions/9132715/strange-behavior-with-isset-returning-true-for-an-array-key-that-does-not-exis