qt5 - Qt: QNetworkAccessManager dont send request -

i used qnetworkaccessmanager handle send http request:

void f() {         qnetworkrequest request( qurl( address ) );         qnetworkaccessmanager mng;     mng.get(request);     //qeventloop().exec();     } void main() {     ...     f();     ... } 

if without line qeventloop().exec();, app not send request. if line qeventloop().exec();, will. don't understan why?
can clear me?
thank much! (p/s: have seen link: sending http request using qnetworkaccessmanager)

void f()     {             static qnetworkrequest request( qurl( address ) );             static qnetworkaccessmanager mng;     mng.get(request); } void main() {     ...     f();     ... } 

i think because qnetworkaccessmanager asynchronous , need time send request. require, url, query, ... destroyed when out of scope. -> need in scope when qnetworkaccessmanager send request (use qeventloop().exec(); ) or let require, url, query, ... persistent (declare static).