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PHP $_POSTis a super global variable that can contain key-value pairs of HTML form data submitted through the post method. We will learn different ways to check $_POSTif a and contains some data in this article. These methods will use isset(), empty()and empty string checks.

Check $_POSTif exists inisset()

isset()The function is a PHP built-in function that can check if a variable is set and not NULL. Also, it works with arrays and array keys. PHP $_POSThas array keys included so isset()it can handle it.

To check $_POSTif an exists, pass it as the value to isset()the function. Also, you can check if the user submitted a specific form input. If the user submitted a form input, it will $_POSTbe available in , even if it is empty.

The HTML below gives us something to work with. It has a form field with a pre-populated name field.

<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
	<label>First Name</label>
	<input type="text" name="first_name" value="DelftStack">
	<input type="submit">
</form>

When you click the submit button, the following PHP will check $_POSTif :

<?php
    if (isset($_POST['first_name'])) {
        $first_name = $_POST['first_name'];
        echo $first_name;
    }
?>

Output:

DelftStack

Use Empty()the function to check $_POSTif

You can empty()check for the existence of using the function $ _POST. However, empty()the function will return if true:

• When all $_POSTvalues ​​are empty strings
• Parameter is zero

The following HTML is the same as the previous one, this time with different names:

<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
    <label>First Name</label>
    <input type="text" name="first_name" value="Mathias Jones">
    <input type="submit">
</form>

The next code block shows you how to use empty()the function check $_POST:

<?php
    if (!empty($_POST)) {
        $first_name = $_POST['first_name'];

        echo $first_name;
    }
?>

Output:

Mathias Jones

Check $_POSTif function exists isset()and empty string check

If the value of $_POST is an empty string, isset()the function returns true, but for a NULL value, it will return false. If you try to print the value of isset($_POST['x']) = NULLand isset($_POST['x']) = '', in both cases you will get an empty string.

Therefore, you will need to check for empty strings. isset()The combination of and empty string check eliminates $_POSTthe possibility that contains an empty string before you process its data.

In the next code block, we have an HTML to work with:

<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
    <label>First Name</label>
    <input type="text" name="first_name" value="Mertens Johanssen">
    <input type="submit">
</form>

Check $_POSTif :

<?php
    if (isset($_POST['first_name']) && $_POST['first_name'] !== "") {

        $first_name = $_POST['first_name'];

        echo $first_name;
    }
?

Output:

Mertens Johanssen

Checks $_POSTif there is a negation operator

The negation operator (!) turns a true statement into a false one and a false statement into a true one. Therefore, you can use the negation operator to check $_POSTif . To check $_POST, add the negation operator to the if-else statement.

In the first part, if $_POSTis empty, you can stop processing its data. In the second part of the condition, you can process the data.

First, the HTML:

<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
    <label>First Name</label>
    <input type="text" name="first_name" value="Marcus Alonso">
    <input type="submit">
</form>

The next code block demonstrates using the negation operator to check for $_ POSTthe existence of .

<?php
    if (!$_POST) {
        echo "Post does not exist";
    } else {
        $first_name = $_POST['first_name'];

        echo $first_name;
    }
?>

Output:

Marcus Alonso