PHP empty (), Isset (), is_null () function Usage Example _php tutorial

In PHP empty (), Isset (), Is_null () Three functions are similar to many friends, but let's just think about it as if it were different, a null value, whether it was a variable, whether it was null, let me give an example.

Many people for PHP empty (), Isset () and Is_null () three functions of the use of fuzzy, the online data is also a lot, but may not be able to speak clearly, the following gives a test example, for understanding the difference between these three functions will have great benefits.

The types of tests are as follows:

$a;
$b = false;
$c = ";
$d = 0;
$e = null;
$f = Array ();
?>

Empty ()

The code is as follows	Copy Code
Var_dump (Empty ($a)); Var_dump (Empty ($b)); Var_dump (Empty ($c)); Var_dump (Empty ($d)); Var_dump (Empty ($e)); Var_dump (Empty ($f)); ?> Output BOOL (TRUE) BOOL (TRUE) BOOL (TRUE) BOOL (TRUE) BOOL (TRUE) BOOL (TRUE)

As you can see from the code, empty () outputs true as long as the data type is empty or false.

Isset ()

The code is as follows	Copy Code
Var_dump (Isset ($a)); Var_dump (Isset ($b)); Var_dump (Isset ($c)); Var_dump (Isset ($d)); Var_dump (Isset ($e)); Var_dump (Isset ($f)); ?> Output BOOL (FALSE) BOOL (TRUE) BOOL (TRUE) BOOL (TRUE) BOOL (FALSE) BOOL (TRUE)

You can see that isset () can only be used to determine if it is null and undefined.

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

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:

The code is as follows	Copy Code
$id = 0; Empty ($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:

The code is as follows	Copy Code
if (empty ($id)) $id = 1; -If id=0, the ID will also be 1 if (!isset ($id)) $id = 1; -If id=0, the ID will not be 1

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

The code is as follows	Copy Code
if (empty ($id)) $id = 1; Print $id; Get 1 if (!isset ($id)) $id = 1; Print $id; Get 0

Is_null ()

The code is as follows	Copy Code
Var_dump (Is_null ($a)); Var_dump (Is_null ($b)); Var_dump (Is_null ($c)); Var_dump (Is_null ($d)); Var_dump (Is_null ($e)); Var_dump (Is_null ($f)); ?> Output BOOL (TRUE) BOOL (FALSE) BOOL (FALSE) BOOL (FALSE) BOOL (TRUE) BOOL (FALSE)

Is_null literally means it.

This shows that empty () can be used to determine whether all data types are empty or false, and is_null is basically the same as isset, and can only be used to determine if null and undefined.

And then I'll attach a table to you.

The following table can clearly explain the relationship between them:

Variable Empty is_null isset
$a = "" True false True
$a =null true True false
var $a true true false
$a =array () True false true
$a =false true false true
$a =15 false False true
$a =1 false False true
$a =0 true false true
$a = "0" true false true
$a = "true" false false true
$a = "false" false false true

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