How php checks whether a variable is set

Php how to check whether a variable is set, for this question, this article introduces the corresponding analysis and solution in detail, hoping to help more partners who want to solve this problem to find a more simple and easy way.

In php, you can use the isset () function to check whether a variable is set, which can be used to detect whether the variable is set and not NULL, with the syntax "isset ($var)"; if the specified variable exists and is not NULL, TRUE is returned, otherwise FALSE is returned.

Operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

Php checks whether a variable is set

Using the isset () function, this function detects whether the variable is set and is not NULL.

Grammar

Bool isset (mixed $var [, mixed $...])

Parameter description:

Var: the variable to be detected.

If you pass in more than one parameter at a time, isset () returns TRUE only if all the parameters are set, and the calculation stops immediately when it encounters an unset variable from left to right.

Return value: returns TRUE if the specified variable exists and is not NULL, otherwise returns FALSE.

Example:

The output is as follows:

The variable has been set. Bool (true) bool (true) bool (false) bool (false) bool (false)

Note: if you have released a variable using unset (), the isset () judgment will return FALSE.

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