深入理解php中ob_flush与flush的区别

ob_start();
echo '1';
ob_flush();//输出php缓存并刷新
echo '2';
ob_flush();//输出php缓存并刷新
$cc = ob_get_contents();
ob_end_clean();
var_dump($cc);
?>

输出： 12string(0) ""

测试2：

ob_start();
echo '1';
flush();     //输出apache缓存并刷新
echo '2';
flush();     //输出apache缓存并刷新
$cc = ob_get_contents();
ob_end_clean();
var_dump($cc);
?>

输出: string(2) "12"

测试3：

ob_start();
echo '1';
ob_flush();//输出php缓存并刷新
flush();//输出apache缓存并刷新
echo '2';
ob_flush();//输出php缓存并刷新
flush();//输出apache缓存并刷新
$cc = ob_get_contents();
ob_end_clean();
var_dump($cc);
?>

输出: 12string(0) ""

测试4，

ob_start();
echo '1';
flush();//输出apache缓存并刷新
ob_flush();//输出php缓存并刷新
echo '2';
flush();//输出apache缓存并刷新
ob_flush();//输出php缓存并刷新
$cc = ob_get_contents();
ob_end_clean();
var_dump($cc);
?>

输出: 12string(0) ""