'class QMutex' has no member named 'EnterCriticalSection'

Question

I'm using QT 4.8 and whenever i do a simple usage of QMutex, I get the compilation error of: 'class QMutex' has no member named 'EnterCriticalSection'

Sample:

void classA::write (int x)
{
   mutex->lock()
   ... do something
   mutex->unlock()
}

mutex is defined as a member in the class and initialized in the header.