The difference between PHP isset () and Empty ()

This article mainly introduces the PHP isset () and empty () the use of the difference, has a certain reference value, now share to everyone, the need for friends can refer to

When using PHP to write a page program, I often use the variable handler function to determine the PHP page trailing parameters of a variable value is empty, at the beginning I used to use the empty () function, but found some problems, so instead of using the isset () function, the problem is no longer.

As the name implies, empty () determines whether a variable is "empty" and isset () determines whether a variable has been set. It is this so-called "as the name implies", so I began to take some detours: when a variable value equals 0 o'clock, empty () will also be set (True), so there will be some accidents. Originally, Empty () and isset () are variable-handler functions, which are used to determine whether variables have been configured, but they have a certain difference:Empty also detects whether the variable is null and zero. When a variable value of 0,empty () considers the variable equal to NULL, it is equivalent to no setting.

For example, the detection of $id variables, when $id = 0 o'clock, with empty () and isset () to detect whether the variable $id is configured, both will return a different value--empty () think that there is no configuration, isset () can get the value of $id:

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

This means that when we use the variable handler function, when the variable may appear with a value of 0, use empty () to be careful, it is wiser to replace it with Isset.

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

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

The following code can be run separately to detect the above inference:

if (empty ($id)) $id = 1; Print $id; Get 1 if (!isset ($id)) $id = 1; Print $id; Get 0

To say their connection, the common point is that empty () and isset () are variable processing functions, the role is to determine whether the variables have been configured, it is because they have a large similarity in the process of variables, it leads to lack of understanding of their relationship. From the two functions of empty () and isset () alone, it would make people more confused and take a different angle. Empty () and Isset () handle objects with no outside defined variables, 0, empty strings.

If the variable is 0, empty () returns True,isset () to return true;

If the variable is an empty string, empty () returns True,isset () to return true;

If the variable is undefined, empty () returns True,isset () returns flase;

Empty () is explained in the manual as follows:

description bool Empty (mixed Var)

If Var is a non-null or nonzero value, empty () returns FALSE. In other words, "", 0, "0", NULL, FALSE, Array (), Var $var; and objects that do not have any properties will be considered empty and return TRUE if Var is empty.

The Isset () is explained in the manual as follows:

Isset () detects if the variable is set

description bool Isset (mixed var [, mixed Var [, ...])

Returns TRUE if Var exists, otherwise FALSE is returned.

If a variable has been freed with unset (), it will no longer be isset (). If you use Isset () to test a variable that is set to NULL, FALSE is returned. Also note that a null byte ("s") is not equivalent to a null constant in PHP.

Warning: isset () can only be used for variables, because passing any other parameter will result in parsing errors. To detect if a constant is set, use the defined () function.

You can use the Isset function when you want to determine if a variable has been declared

When you want to determine whether a variable has been given data and is not empty, you can use the empty function

When you want to determine if a variable exists and is not empty first isset function again with the empty function