PHP isset and unset Functions

Purpose of isset in PHP

That means it determines if a variable is assigned a value and is not null.

Also, the isset PHP function checks if the given variable is not unset by using the unset function.

Syntax of using the isset function

This is how you can use the isset function:

The isset function returns true if a variable is set and false if it is not or is being unset by using the unset function.

Example of using isset in PHP

In this example, we have simply declared a string variable and assigned it “” value.

Although it does not contain any character, as it is being set, see the coce and output below:

$str_isset = "";
$bol_isset = isset($str_isset);

If ($bol_isset){
   echo "The variable is set";
}
else {
    echo "The variable is not set";   
}

Result:

You can see, the output is “The variable is set” although it contains zero characters. The isset function will return as true because we had set it.

Example without setting a variable

In that example, we will not assign it any value, not even “”. We have just declared that string variable and see the output:

$str_isset = "";
$bol_isset = isset($str_isset);

If ($bol_isset){
   echo "The variable is set";
}
else {
    echo "The variable is not set";   
}

Output:

So that resulted in the “The variable is not set”, even though we had declared it. Now look at an example of isset with 2 variables.

isset example with two variables

As mentioned earlier, you can specify one or more variables in the isset function.

However, if any variable is not set or has been sunset by using the unset function or it is a Null, it will return as false.

In that case, even if other variables are set, the function still returns the false.

See the following example and output:

$str_isset = "";
$str_2;
$bol_isset = isset($str_isset,$str_2);

If ($bol_isset){
   echo "The variables are set";
}
else {
    echo "The variables are not set";   
}

Output:

You see although we have set the first variable while the second variable was only declared and not given any value. The isset function returned false with the output:

An example with array elements

Not only you can use isset function with simple variables to determine if those are set or not but you can also use it to check array elements as well.

See the example code/output:

$salaries = array(); 
$salaries["Anna"] = 5000;
$salaries["John"] = null;
$salaries["Aamir"] = 10000;

foreach($salaries as $key_arr => $val_arr){
    if (isset($val_arr)){
    echo "(This is true/set) " . $key_arr . " = " .$val_arr ."<br />";
    }
    else{
        echo "(This is false/not set) " . $key_arr . " = " .$val_arr ."<br />";
    }
}

Output:

Syntax of unset function

Following is the general syntax to use PHP unset function:

An unset example

In this example, a variable was declared and assigned a value. After that, it was unset by using the unset function, so it was destroyed.

See the code and output before and after using the unset function.

$str_isset = "The isset example";
$bol_isset = isset($str_isset);

If ($bol_isset){
   echo "The variable is set </BR>";
}
else {
    echo "The variable is not set </BR>";   
}
//Using unset function
unset ($str_isset);
$bol_isset = isset($str_isset);
If ($bol_isset){
   echo "The variable is set";
}
else {
    echo "The variable is not set";   
}

Output:

Why do we use isset and unset functions

There are a few solid reasons to use the isset function in PHP programs.

• One of the reasons is that while you use a lot of variables in your PHP programs, it is generally a good practice to check variables if they are set or not before using them.
• Basically, it checks whether a variable or index exists or not.
• PHP generates notice if you think a variable exists while actually, it is not.
• By using the isset function, you may avoid any unwanted notices.

The unset function

• The unset function of PHP is used to destroy a given variable.

How to use PHP isset function

You have to specify a variable to set inside the isset function.

As isset returns a Boolean value (true or false), you can assign it to a Boolean variable as shown below:

You may specify more than one variables in the isset function. In that case, the isset function will return true if all variables are set otherwise it will return false.

The examples are shown in the above section.

Using unset function

The unset function is quite simple to use. Simply specify the variable(s) name inside the unset function as follows: