PHP null var存在[重复]

Question

Possible Duplicate:
Check if value isset and null

If I have $v = NULL; how can I check that $v is exists and it's NULL?

isset($v) => false //because of NULL, but $v exists

Answer 1

You can’t, null is equivalent to a non-existing variable:

A variable is considered to be null if:

• it has been assigned the constant NULL.
• it has not been set to any value yet.
• it has been unset().

Only for arrays you can check whether a key exists although its value is null using array_key_exists.