PHP isset () and empty () the difference between the use of a detailed

PHP's Isset () function is commonly used to detect whether a variable is set

Format: bool Isset (mixed var [, mixed Var [, ...])
Function: Detect whether the variable is set
return value:
Returns FALSE if the variable does not exist
Returns FALSE if the variable exists and its value is null
Returns TURE if the variable exists and the value is not NULL
Returns TRUE if each item meets the previous requirement when checking multiple variables at the same time, otherwise the result is FALSE
Version: PHP 3, PHP 4, PHP 5
More information:
After you use Unset () to release a variable, it will no longer be isset ().
PHP functions Isset () can only be used for variables, and passing any other parameter will result in parsing errors.
Detects if a constant is set to use the defined () function.

The empty () function of PHP determines whether the value is null

Format: bool Empty (mixed Var)
function: Check if a variable is empty
return value:
Returns TRUE if the variable does not exist
If the variable exists and its value is "", 0, "0", NULL, FALSE, Array (), Var $var; and objects that do not have any properties, the TURE is returned.
If the variable exists and the value is not "", 0, "0", NULL, FALSE, Array (), Var $var; And an object that does not have any properties, it returns FALSE
Version: PHP 3, PHP 4, PHP 5
More information:
The return value of empty () =! (Boolean) Var, but does not produce a warning message because the variable is undefined. See Convert to Boolean for more information.
Empty () can only be used for variables, and passing any other parameter will cause Paser error and terminate the run.
Detects if a constant is set to use the defined () function.
Example: A simple comparison of empty () with Isset ()

PHP Code

<?php $var = 0;   The result is true because the $var is empty if (Emptyempty ($var)) {echo ' $var is either 0 or not set at all ';   }//The result is false because $var has set the IF (!isset ($var)) {echo ' $var is not set to all '; }; 

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 be aware of a NULL byte ("?" ) is not equivalent to the NULL constant of 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

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