wp_get_current_user（）无法识别

Question

我试图将当前用户ID从Wordpress网站添加到我设置的表中。来自输入的所有其他值都很好，但是当我尝试这段代码时我收到了php错误：

$link = mysqli_connect("localhost", "XXXXXX", "XXXXXX", "XXXXXX");

if($link === false){
die("ERROR: Could not connect. " . mysqli_connect_error());
}

$latLng = mysqli_real_escape_string($link, $_POST['latLng']);
$title = mysqli_real_escape_string($link, $_POST['title']);
$type = mysqli_real_escape_string($link, $_POST['type']);

$current_user = wp_get_current_user(); 
$WP_id = $current_user->ID;

$sql = "INSERT INTO  `user_locations` (  `id` ,  `WP_id` , `latLng` ,      `type` ,  `title` ) VALUES ('', '$WP_id', '$latLng',  '$type',  '$title')";

if(mysqli_query($link, $sql)){
header("Location: leaflet-test-page");
} else{
    echo "ERROR: Could not able to execute $sql. " . mysqli_error($link);
}

mysqli_close($link);

错误是：

Fatal error: Call to undefined function wp_get_current_user() in /home/XXXXX/public_html/XXXXXX/insert.php on line 17

任何帮助确定我收到此错误的原因将不胜感激。