$id=$_POST['id'];

Question

Why is it always written like this in the editor! No., when running, it always says that it is not defined

Answer 1

I feel that there is no id in add.html, so I feel that that line of code can be omitted.

Answer 2

Check whether

$_POST['id']

exists

Answer 3

if（isset（$_POST['id']）{
$id=$_POST['id'];
}

First determine whether $_POST['id'] exists before using it

Answer 4

If there is no value in the post, of course it is undefined. If you use a from form to submit to a page and receive the id value, it will not be reported as undefined

Answer 5

Please post the error message

Answer 6

You can block warning level errors. Some versions of PHP will prompt warning errors that POST parameters do not exist. Officially launched to block non-fatal errors.