Use static in php custom functions

function sendHeader($num, $rtarr = null) {
static $sapi = null;
if ($sapi === null) {
$sapi = php_sapi_name();
}
return $sapi++;
?>

When I looked at the PW source code, I found that the static keyword was used in the setHeader() function. It was strange. It had never been used like this before.

static is used in functions. After declaring a variable once, if the function is called again, it will continue at the initial value. For example, $sapi will be accumulated.

echo sendHeader(1)."";
echo sendHeader(2)."";
echo sendHeader(3)." ";
?>

Output result: apache2handler apache2handles apache2handlet

Instructions: It is somewhat similar to global, but the difference is the scope. static can only be used on this function.