I have an update function in my app - it downloads and verifies the installer (a setup.exe, created with NSIS). To actually kick off the update, I have simply been doing:
QString path = .. absolute path to the downloaded file ...
QProcess::startDetached(path, QStringList());
This works fine on XP - but on Vista and Win7, nothing happens once the download completes. If I browse to the downloaded update and run it manually, it works fine. I assume what's happening is that UAC is blocking the installer at CreateProcess time, but this is where my knowledge runs out.
Additional complication - when I'm running a debug build from the command line, the steps above work - I get the UAC prompt and can run the installer. It's the release builds, started form the start menu/shortcut, which have the issue - I assume there's a difference in the auth token when running from a command shell.
If you are not admin and you call CreateProcess() on a .exe with a "Vista" manifest (or no manifest, but a .exe that windows detects as an installer (This includes NSIS)) the call fails, you need to use ShellExecute[Ex](). ShellExecute will trigger UAC prompt if required...