在使用 set_error_handler() 改变错误处理函数之后，此函数可以 用于还原之前的错误处理程序
if (null === $prev = set_error_handler(array($handler, 'handleError'))) {
restore_error_handler();
// Specifying the error types earlier would expose us to https://bugs.php.net/63206
set_error_handler(array($handler, 'handleError'), $handler->thrownErrors | $handler->loggedErrors);
$handler->isRoot = true;
}举例说明
<?php
function unserialize_handler($errno, $errstr)
{
echo "Invalid serialized value.\n";
}
$serialized = 'foo';
set_error_handler('unserialize_handler');
$original = unserialize($serialized);
restore_error_handler();
?>