Php judges the difference between if ($ _ POST [submit]) and if (isset ($ _ POST [submit]) when submitting a form.

Use if (isset ($ _ POST ['submit ']) {
}
Difference between if ($ _ POST [submit]) and if (isset ($ _ POST [submit]) when submitting a form

The first method produces a warning, and the second method is more rigorous.
In addition, it is best to add single quotes to the key name of POST, so the efficiency is slightly higher (about 3-4 times ).
If this variable is set, true is returned.

In PHP, what does if (isset ($ _ POST ['submit ']) mean?
Isset -- check whether the variable is set

Determine whether post data is submitted
Copy codeThe Code is as follows:
If (isset ($ _ POST ["submit"]) {
Echo "submitted ";
} Else
{
Echo "submit is no come ~ ";
}