Getting confused with empty, isset, !empty, !isset

I have the following which doesn't work properly as $_GET['category'] can also equal 0.

if ( empty( $_GET['category'] ) ){
    // do something
} else {
    // do something else
}

How do I re-write this if statement to do 3 different things

Do something if $_GET['category'] does not exist at all

Do something if $_GET['category'] == 0

Do something if $_GET['category'] == something other than "does not exist" and 0.

I've tried different combinations of empty() , !empty() , isset() , !isset() but I'm not getting the results I'm after. I'm probably doing the wrong combinations...

---

This isn't really hard to do: isset is the method you need.

if (!isset($_GET['category'])) {
    // category isn't set
} elseif ($_GET['category'] === '0') {
    // category is set to 0
} else {
    // category is set to something other than 0
}

Note that I have compared for exact equality to the string '0' , because GET and POST variables are always strings (or occasionally arrays) and never numbers when PHP first receives them.

---

if (!isset($_GET['category']))
{
    1. Do something if $_GET['category'] does not exist at all
}
elseif ($_GET['category'] == 0)
{
    2. Do something if $_GET['category'] == 0
}
elseif (isset($_GET['category']) && ($_GET['category'] != 0)
{
    3. Do something if $_GET['category'] == something other than "does not exist" and 0.
}

我的括号可能稍微有些偏差，但希望能帮助你。

---

有这种情况下的filter_input功能。

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