Why Does My HTML Input Value Attribute Truncate at Spaces When Using PHP?

Value Attribute Delimiter Confusion with Spaces in Input Data

When populating an HTML input element's value attribute using PHP, spaces can cause unexpected behavior. Consider the following example:

<input type="text" name="username"
<?php echo (isset($_POST['username'])) ? "value = ".$_POST["username"] : "value = \"\""; ?> />

If a user enters "Jonathan" as the username, it is displayed correctly. However, if they enter "Big Ted", only "Big" is displayed after submitting the form.

The issue lies in the handling of spaces in the value attribute. Without proper delimiters, the space becomes an attribute separator, causing the subsequent text to be treated as additional attributes.

To resolve this, the value attribute must be quoted. Using double quotes ensures that spaces are included within the value rather than splitting it into separate attributes:

<input value="<?php echo (isset($_POST['username'])) ? htmlspecialchars($_POST['username']) : ''; ?>" />

Additionally, the htmlspecialchars() function should be used to escape any special characters, including quotes, to prevent cross-site scripting (XSS) attacks.

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