Sonar-cxx (here: cxx-v0.9.7) can be installed into a SonarQube Docker Image like follows:
sudo docker search sonarqube
sudo docker pull sonarqube
sudo docker run -d --name sonarqube -p 9000:9000 -p 9092:9092 sonarqube # runs under http://localhost:9000
wget https://github.com/SonarOpenCommunity/sonar-cxx/releases/download/cxx-0.9.7/sonar-cxx-plugin-0.9.7.jar # get sonar-cxx v0.9.7
sudo docker cp ./sonar-cxx-plugin-0.9.7.jar sonarqube:/opt/sonarqube/extensions/plugins/sonar-cxx-plugin-0.9.7.jar # install plugin into plugin directory
sudo docker restart sonarqube