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
$var = 0;
The result is true because the $var is empty
if (empty ($var)) {
Echo ' $var is either 0 or isn't set at all ';
}
The result is false because the $var has been set
if (!isset ($var)) {
Echo ' $var is not set at all ';
}
?>

Note: Because this is a language structure and not a function, it cannot be called by a variable function.
Note: empty () detects only variables and detects anything that is non-variable will result in parsing errors. In other words, the statement behind will not work: Empty (Addslashes ($name)).

Here is the code for a detailed example of the isset and empty functions that have been tested by the Scripting House:

<?php
Error_reporting (E_all);
Echo ' <B> undefined $var</b><br> ';
echo "Isset test:<br>";
if (Isset ($var))
{
Echo ' variable $var exists!<br> ';
}
echo "Empty test:<br>";
if (empty ($var)) {
echo ' variable $var value is null <Br> ';
}
Else
{
echo ' variable $var value is not empty <Br> ';
}
echo "Variable direct test:<br>";
if ($var) {
Echo ' variable $var exists!<br> ';
}
else {
echo ' variable $var does not exist!<br> ';
}
Echo '----------------------------------<br> ';
echo ' <B> $var = \ ' \ ' </b><Br> ';
echo "Isset test:<br>";
$var = ";
if (Isset ($var))
{
Echo ' variable $var exists!<br> ';
}
echo "Empty test:<br>";
if (empty ($var)) {
echo ' variable $var value is null <Br> ';
}
Else
{
echo ' variable $var value is not empty <Br> ';
}
echo "Variable direct test:<br>";
if ($var) {
Echo ' variable $var exists!<br> ';
}
else {
echo ' variable $var does not exist!<br> ';
}
Echo '----------------------------------<br> ';
echo ' <B> $var = 0</b><br> ';
Echo ' isset test:<br> ';
$var = 0;
if (Isset ($var))
{
Echo ' variable $var exists!<br> ';
}
echo "Empty test:<br>";
if (empty ($var)) {
echo ' variable $var value is null <Br> ';
}
Else
{
echo ' variable $var value is not empty <Br> ';
}
echo "Variable direct test:<br>";
if ($var) {
Echo ' variable $var exists!<br> ';
}
else {
echo ' variable $var does not exist!<br> ';
}
Echo '----------------------------------<br> ';
echo ' <B> $var = Null</b><br> ';
Echo ' isset test:<br> ';
$var = null;
if (Isset ($var))
{
Echo ' variable $var exists!<br> ';
}
echo "Empty test:<br>";
if (empty ($var)) {
echo ' variable $var value is null <Br> ';
}
Else
{
echo ' variable $var value is not empty <Br> ';
}
echo "Variable direct test:<br>";
if ($var) {
Echo ' variable $var exists!<br> ';
}
else {
echo ' variable $var does not exist!<br> ';
}
Echo '----------------------------------<br> ';

echo ' <B> $var = ' php ' </b><Br> ';
Echo ' isset test:<br> ';
$var = "PHP";
if (Isset ($var))
{
Echo ' variable $var exists!<br> ';
}

echo "Empty test:<br>";
if (empty ($var)) {
echo ' variable $var value is null <Br> ';
}
Else
{
echo ' variable $var value is not empty <Br> ';
}
echo "Variable direct test:<br>";
if ($var) {
Echo ' variable $var exists!<br> ';
}
else {
echo ' variable $var does not exist!<br> ';
}
?>

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