Why Am I Getting the \'Undefined variable: HTTP_POST_FILES\' Error When Uploading Files in PHP?

Upload a File Using PHP: Troubleshooting "Undefined Variable: HTTP_POST_FILES" Error

Uploading files to a server using PHP can be a simple process. However, it's essential to address any errors that may arise during the process.

Problem:
An error occurs when attempting to upload a file using PHP: "Notice: Undefined variable: HTTP_POST_FILES".

Cause:
The $HTTP_POST_FILES variable refers to the global array that stores uploaded file information. However, it has been deprecated since PHP 4.1.0 and is not recommended for use.

Solution:
Modern PHP versions expect a different structure for accessing uploaded file data. Instead of $HTTP_POST_FILES, use the following methodology:

$_FILES["file_name"]["key"]

Where:

• file_name is the name of the input field where the file was selected.
• key is the specific aspect of the file being accessed (e.g., "name", "type", "size", "tmp_name").

Example Code:

The following improved PHP code adheres to best practices for file uploading:

$target_dir = "upload/";
$target_file = $target_dir . basename($_FILES["filename"]["name"]);
$imageFileType = strtolower(pathinfo($target_file, PATHINFO_EXTENSION));
$allowedTypes = ['jpg', 'png'];

if (isset($_POST["submit"])) {
    // Check file type
    if (!in_array($imageFileType, $allowedTypes)) {
        echo "Type is not allowed";
    }
    // Check if file already exists
    elseif (file_exists($target_file)) {
        echo "Sorry, file already exists.";
    }
    // Check file size
    elseif ($_FILES["filename"]["size"] > 5000000) {
        echo "Sorry, file is too large.";
    } else {
        // Upload file
        if (move_uploaded_file($_FILES["filename"]["tmp_name"], $target_file)) {
            echo "File uploaded successfully.";
        }
    }
}

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