$_FILES remains empty - php

Question

I'm trying to add an upload feature in an existing Wordpress plugin. But the file seems not to load. I use this code in the form:
<form action="" method="post" enctype="multipart/form-data">
<label for="file">Filename:</label>
<input type="file" name="file" id="file"><br>
// other code of existing plugin.
<input type="submit" value="plugin submit" id="plugin submit" name="plugin submit">
</form>
Then in the function of the plugin I put the test line for knowing what happens:
if ($_FILES["file"]["error"] > 0)
{
echo "Error: " . $_FILES["file"]["error"] . "<br>";
}
else
{
echo "Upload: " . $_FILES["file"]["name"] . "<br>";
echo "Type: " . $_FILES["file"]["type"] . "<br>";
echo "Size: " . ($_FILES["file"]["size"] / 1024) . " kB<br>";
echo "Stored in: " . $_FILES["file"]["tmp_name"];
}
I enter in else branch but all fields are empty. What am I missing?

Answer 1

You will hit the else branch even if $_FILES is undefined.
You can first check that the user uploaded a file.
is_uploaded_file()
Returns TRUE if the file named by filename was uploaded via HTTP POST.
You can use somthing like:
if(is_uploaded_file($_FILES['file']['tmp_name'])
But since it seems this will not return TRUE in your case I must ask - since your form is POSTing to the same page that it is on - is your PHP code at the top of the page where your form resides? If that is the case don't you find it odd that it outputs the blank upload information even before you upload?