could not upload file through multidimensional file input

[shane07]

Here is the html for file input

<input type="file" name="edit[image]" id="edit-image" />

I could not upload file from this input.

When I tried print_r($_FILES), it outputs an empty array.

I also tried

$sth=$_FILES['edit[image]']['name']

and

$sth=$_FILES['edit']['name']['image']

but could not access that input, it says undefined index.