Targeting Windows, I'd use Win32's CreateProcess directly, as the exec/system stuff is a real mess and I end up carefully setting things up to take the program path I wanted.

I think "DETACHED_PROCESS" vs DETACHED_PROCESS (the constant) is the problem with that one.

In any case, whether it (by default) waits for the process to complete depends on the subsystem used by the target executable. Console programs wait, Win32 programs don't.