改变cmd的路径环境变量。exe与QProcessEnvironment

I want to start cmd.exe from a Qt app with a specific PATH set. I insert "Path" in QProcessEnvironment and set that environment to QProcess. Then I startDetached "cmd". On the command prompt, the path is the same as the from the calling app, not what I just set. Did I miss something? I use Qt 5.2.0 with mingw and Qt-creator 3.0.0 on windows 8.1.sI want to start cmd.exe from a Qt app with a sp