Php empty (), isset (), is_null () function usage example

In php, empty (), isset (), and is_null () functions are similar to each other in many of our friends, but it seems that they are different. A null value, whether a variable is null or not. The following is an example.

Many people have vague usage of PHP empty (), isset (), and is_null () functions. There are also a lot of information on the Internet, but it may not be clear, the following is a test example, which will be of great benefit to understanding the differences between the three functions.

 

The test type is as follows:

  $;
$ B = false;
$ C = '';
$ D = 0;
$ E = null;
$ F = array ();
?>

 
Empty ()
 

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Var_dump (empty ($ )); 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)

The Code shows that empty () Outputs true if the data type is null or false.

Isset ()
 

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Var_dump (isset ($ )); 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)

We can see that isset () can only be used to determine whether it is NULL or not.

 
Warning: isset () can only be used for variables, because passing any other parameter will cause a parsing error. To check whether a constant has been set, use the defined () function.
You can use the isset function to determine whether a variable has been declared.
You can use the empty function to determine whether a variable has been assigned data and is not empty.
To determine whether a variable exists and is not empty, use the isset function and the empty function.

For example, if the $ id variable is detected and $ id = 0, empty () and isset () are used to check whether the variable $ id has been configured, the two will return different values -- empty () think that there is no configuration, isset () can get the value of $ id:

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$ Id = 0; Empty ($ id )? Print "It's empty.": print "It's $ id ."; // Result: It's empty. Print" "; ! Isset ($ id )? Print "It's empty.": print "It's $ id ."; // Result: It's 0.

This means that when we use a variable to process a function, when the variable may have a value of 0, we should be careful when using empty (). In this case, it is more wise to replace it with isset.

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

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If (empty ($ id) $ id = 1;-if id = 0, the id is also 1 If (! Isset ($ id) $ id = 1;-if id = 0, id is not 1

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

 

Is_null ()
 

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Var_dump (is_null ($ )); 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.

It can be seen that empty () can be used to determine whether all data types are NULL or false, while is_null is basically the same as isset and can only be used to determine whether it is NULL or undefined.

A table will be attached to you later.

The following table clearly describes the relationship between them:

Empty is_null isset
$ A = "true false true
$ A = null true false
Var $ a true false
$ A = array () true false true
$ A = false true
$ A = 15 false true
$ A = 1 false true
$ A = 0 true false true
$ A = "0" true false true
$ A = "true" false true
$ A = "false true