What is difference between isset() and empty()

In PHP, isset and empty are used to check whether a variable has a value or not, but they have different definitions and behaviors.

isset() is a function that returns true if the variable exists and is not null. It checks whether a variable has been set or not. If the variable exists and has any value other than null, isset() returns true. For example:

$var = "Hello World!";
if (isset($var)) {
    echo "The variable is set.";
}

In the above example, since $var is set to a string value, isset($var) returns true, and the message “The variable is set.” will be printed.

On the other hand, empty() is a function that returns true if the variable is empty or not set at all. It checks whether a variable has been set and has a non-empty value or not. If the variable does not exist, or if its value is null, an empty string, an empty array, false, or a zero integer, empty() returns true. For example:

$var = "";
if (empty($var)) {
    echo "The variable is empty.";
}

In the above example, since $var is set to an empty string, empty($var) returns true, and the message “The variable is empty.” will be printed.

So, the main difference between isset() and empty() is that isset() checks whether a variable is set or not, while empty() checks whether a variable is set and has a non-empty value or not.