Determines whether PHP variables are defined and empty

Isset () [1]

ReturnsTrueIfVaR
Exists and has value other
ThanNull,FalseOtherwise.

The input can be multiple variables. Only when all the variables are true returns true.

 

Empty () [2]

 

ReturnsFalseIfVaR
Has a non-empty
And non-zero value.

The following things are considered to be empty:

• "" (An empty string)
• 0 (0 as an integer)
• "0" (0 as a string)
• Null
• False
• Array () (an empty array)
• VaR $ var; (a variable declared, but without
  Value in a class)

 

The input can only be a variable.

 

Is_null () [3]

ReturnsTrueIfVaRIs
Null "href =" http://www.php.net/manual/en/language.types.null.php "> null,False
Otherwise.

 

 

 

A variable is considered to be null "href =" http://www.php.net/manual/en/language.types.null.php "> null if:

• It has been assigned the constantNull.

• It has not been set to any value yet.

• It has been unset ().

Use PHP Functions $ XFor comparison

Expression	GetType ()	Empty ()	Is_null ()	Isset ()	If ($ X) Boolean
$ X = "";	String	True	False	True	False
$ X = NULL;	Null	True	True	False	False
VaR $ X;	Null	True	True	False	False
$ XIs undefined	Null	True	True	False	False
$ X = array ();	Array	True	False	True	False
$ X = false;	Boolean	True	False	True	False
$ X = true;	Boolean	False	False	True	True
$ X = 1;	Integer	False	False	True	True
$ X = 42;	Integer	False	False	True	True
$ X = 0;	Integer	True	False	True	False
$ X =-1;	Integer	False	False	True	True
$ X = "1 ";	String	False	False	True	True
$ X = "0 ";	String	True	False	True	False
$ X = "-1 ";	String	False	False	True	True
$ X = "php ";	String	False	False	True	True
$ X = "true ";	String	False	False	True	True
$ X = "false ";	String	False	False	True	True

 

(The original source is not found in the table above. Please let me know)

 

What if the variable is an object?

Expression	GetType ()	Empty ()	Is_null ()	Isset ()	If ($ X) Boolean
$ X = new object ()	Object	False	False	True	True

 

Refer:

[1] http://php.net/manual/en/function.isset.php

[2] http://www.php.net/manual/en/function.empty.php

[3] http://www.php.net/manual/en/function.is-null.php