php设置文件上传大小

<?php
if ($_FILES['file']['error'] == UPLOAD_ERR_OK) {
    $fileTmpPath = $_FILES['file']['tmp_name'];
    $fileName = $_FILES['file']['name'];
    $fileSize = $_FILES['file']['size'];
    $fileType = $_FILES['file']['type'];
    $fileNameCmps = explode(".", $fileName);
    $fileExtension = strtolower(end($fileNameCmps));

    $allowedExtensions = array("jpg", "jpeg", "png", "gif");
    if (in_array($fileExtension, $allowedExtensions)) {
        if ($fileSize <= 50 * 1024 * 1024) { // 50MB
            $dest_path = 'uploads/' . $fileName;
            if(move_uploaded_file($fileTmpPath, $dest_path)) {
                echo 'File is successfully uploaded.';
            } else {
                echo 'There was some error moving the file to upload directory. Please make sure the upload directory is writable by web server.';
            }
        } else {
            echo 'File size exceeds limit of 50MB';
        }
    } else {
        echo 'Invalid file extension. Only JPG, JPEG, PNG and GIF files are allowed.';
    }
} else {
    echo 'There is some error in the file upload. Please check the following error.<br>';
    echo 'Error:' . $_FILES['file']['error'];
}
?>