Use isset in php with caution to determine whether the array exists with key_PHP tutorial-php Tutorial

In php, use isset with caution to determine whether the array has a key. This article describes how to use isset in php to determine whether an array has a key. After connecting to the code, I don't know if it is a problem with php5.4, or if the code is as follows, I will refer to some examples about how to use isset in php to determine whether the array has a key.

After connecting to the code, I don't know if it's a problem with php5.4, or is it like this...

The code is as follows:
$ A ['hello'] = '123 '; $ A ['XX'] = NULL; Var_dump (isset ($ a ['hello']); // bool (true) Var_dump (isset ($ a ['XX']); // bool (false) # Use this to determine Var_dump (array_key_exists ('XX', $ a); // bool (true)

Bytes. Connect to the code. I don't know if it is a problem with php5.4, or if the code is copied as follows...