Recursion on a static variable

<code class="php"><?php
function test()
{
    static $count = 0;

    echo $count++;
    if ($count < 10) {
        test();
    }
    echo $count--;
}
?></code>

Result: 012345678910987654321
The echo $cont++ in the first half, I can understand why echo $count--it starts from 10. Press from top to bottom, ++ --doesn’t it offset?

Reply content:

<code class="php"><?php
function test()
{
    static $count = 0;

    echo $count++;
    if ($count < 10) {
        test();
    }
    echo $count--;
}
?></code>

Result: 012345678910987654321
The echo $cont++ in the first half, I can understand why echo $count--it starts from 10. Press from top to bottom, ++ --doesn’t it offset?

This is the entry and exit sequence of the stack

If function is called inside, the following cannot be executed until the count>10 function call is completed.

The first 10 recursions did not execute echo $count--;, because the recursive call has not ended yet. Until $count == 10, there will be no more recursion, so it is completed layer by layer Recursive operation