Talking about the difference between empty and isset in PHP

Empty is a value that determines whether the variable value is Non-null or Non-zero. Corresponding NULL definitions include: "" (empty string), 0, "0", NULL, FALSE, Array (), and $var (only declared but not assigned). That is, when the value of the variable is above, empty returns True and the rest returns false.

The isset is to detect whether the variable is set and is not NULL. Variable settings can be in several ways. 1: The simplest is whether the variable is declared and assigned first, and whether there is a corresponding attribute in index or key;3:object in the 2:array.

You can see from the two function definitions above that, in some cases, the two can be public, but the difference is great. In addition, they can only detect variables, and detecting anything that is not variable will result in parsing errors. For example, check the return value of another function directly (empty (Otherfunction ()), and you will see "Fatal error:can ' t use function returned value in write context" Such a mistake.

In addition, isset can check multiple variables at a time, such as: Isset ($var 1, $var 2, $var 3), and the result is false if each of the three values Isset is true.

Test code:

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$sep = "<br/>"; Echo ' Test undeclared var empty: '; Var_dump (Empty ($var)); TRUE Echo $sep. ' Test undeclared var isset: '; Var_dump (Isset ($var)); FALSE $var; Echo $sep. ' Test declared VAR but no set value empty: '; Var_dump (Empty ($var)); TRUE Echo $sep. ' Test declared VAR but no set value isset: '; Var_dump (Isset ($var)); FALSE, the variable declaration is not assigned, and the default value is NULL $var = NULL; Echo $sep. ' Test declared Var and set value NULL empty: '; Var_dump (Empty ($var)); TRUE Echo $sep. ' Test declared Var and set value NULL isset: '; Var_dump (Isset ($var)); FALSE, variable declaration assignment is null $var 1 = '; $var 2 = ' 0 '; $var 3 = 0; $var 4 = FALSE; $var 5 = array (); Echo $sep. ' Test ' empty: '; Var_dump (Empty ($var 1)); TRUE Echo $sep. ' Test ' 0 ' empty: '; Var_dump (Empty ($var 2)); TRUE Echo $sep. ' Test 0 empty: '; Var_dump (Empty ($var 3)); TRUE Echo $sep. ' Test FALSE empty: '; Var_dump (Empty ($var 4)); TRUE Echo $sep. ' Test Array () empty: '; Var_dump (Empty ($var 5)); TRUE Echo $sep. ' Test ', ' 0 ', 0, FALSE, Array () Isset: '; Var_dump (Isset ($var 1, $var 2, $var 3, $var 4, $var 5)); TRUE, the variable affirms and assigns an empty string

The results of the output are:

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Test Undeclared var Empty:bool (true) Test undeclared var isset:bool (false) Test declared Var but no set value empty : bool (true) Test declared Var but no set value Isset:bool (false) Test declared Var and set value NULL empty: BOOL (true) Test declared Var and set value NULL Isset:bool (false) Test ' Empty:bool (true) Test ' 0 ' empty : bool (TRUE) Test 0 Empty:bool (true) Test FALSE Empty:bool (true) Test array () Empty:bool (true) Test ', ' 0 ', 0, FALSE, Array () Isset:bool (true)

For example, to detect $id variables, when $id = 0 o'clock, using empty () and isset () to detect whether the variable $id has been configured, both will return a different value--empty () do not think that the configuration, isset () can get $id value:

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$id = 0; Empty ($id) print "It's empty.":p rint "it's $id." Result: It ' s empty. print "<br>"; !isset ($id) print "It's empty.":p rint "it's $id." Result: It ' s 0.

This means that when we use a variable-handling function, when the variable is likely to have a value of 0, use empty () to be careful, and it's wiser to replace it with Isset.

When the URL tail parameter of a PHP page appears id=0 (for example: test.php?id=0), try to compare:

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if (empty ($id)) $id = 1; -If id=0, ID will also be 1 if (!isset ($id)) $id = 1; -if id=0, id not be 1

You can run the following code separately to detect the above inference:

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if ( Empty ($id)) $id = 1;     print $id;//Get 1     if (!isset ($id)) $id = 1;     print $id;//Get 0