在PHP中的函数之间共享变量而不使用全局变量

function count_calls() {
    static $count = 0;
    $count++;
    echo "This function has been called $count times.\n";
}

count_calls(); // 输出 "This function has been called 1 times."
count_calls(); // 输出 "This function has been called 2 times."
count_calls(); // 输出 "This function has been called 3 times."