Explanations and differences between empty () and isset () in the PHP Manual

Description: boolisset (mixed $ var [, mixed $...]) checks whether the variable is set and is not NULL. If unset () is used to release a variable, it will no longer be isset (). If you use isset () to test a variable that is set to NULL, FALSE is returned. Note that a NULL byte (

Description: bool isset (mixed $ var [, mixed $...]) checks whether the variable is set and is not NULL. If unset () is used to release a variable, it will no longer be isset (). If you use isset () to test a variable that is set to NULL, FALSE is returned. Note that a NULL byte (\ 0

Description

BoolIsset(Mixed$var[, Mixed$...])

Check whether the variable is set and notNULL.

If unset () has been used to release a variable, it will no longer beIsset (). If you useIsset ()TestNULLWill returnFALSE. Note thatNULLByte ("\ 0") Is not equivalent to PHP'sNULLConstant.

If multiple parameters are supplied thenIsset ()Will returnTRUEOnly if all of the parameters are set. Evaluation goes from left to right and stops as soon as an unset variable is encountered.