相关资料：
https://blog.csdn.net/qq_43658314/article/details/109814071 QT学习记录 --- 利用QNetworkConfigurationManager检测网络连接变化
https://www.cnblogs.com/itrena/p/5938377.html QHostInfo类为主机名查找提供了静态函数。
https://www.cnblogs.com/liushui-sky/articles/9474478.html Qt判断网络连接
实例代码：
testNetOnIine.pro
1 QT += core gui 2 QT += network 3 4 greaterThan(QT_MAJOR_VERSION, 4): QT += widgets 5 6 CONFIG += c++11 7 8 # The following define makes your compiler emit warnings if you use 9 # any Qt feature that has been marked deprecated (the exact warnings 10 # depend on your compiler). Please consult the documentation of the 11 # deprecated API in order to know how to port your code away from it. 12 DEFINES += QT_DEPRECATED_WARNINGS 13 14 # You can also make your code fail to compile if it uses deprecated APIs. 15 # In order to do so, uncomment the following line. 16 # You can also select to disable deprecated APIs only up to a certain version of Qt. 17 #DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000 # disables all the APIs deprecated before Qt 6.0.0 18 19 SOURCES += \ 20 main.cpp \ 21 mainwindow.cpp 22 23 HEADERS += \ 24 mainwindow.h 25 26 FORMS += \ 27 mainwindow.ui 28 29 # Default rules for deployment. 30 qnx: target.path = /tmp/$${TARGET}/bin 31 else: unix:!android: target.path = /opt/$${TARGET}/bin 32 !isEmpty(target.path): INSTALLS += target