How to set auto-exposure mode ?

[salocinx]

I am working with OpenCV 3.4.2 and Visual Studio 2015 / C++ on Windows 10.

I can set the exposure of the camera to any value by using this code:

cv::VideoCapture *cap;  
...
cap = new cv::VideoCapture(0);
cap->set(CV_CAP_PROP_EXPOSURE, exposure);   // exposure = [0, 255]

Now I would like to switch to auto-exposure too. How can I set the camera to auto-exposure mode?

I tried the following:

cap->set(CV_CAP_PROP_EXPOSURE, 0);       // not working
cap->set(CV_CAP_PROP_EXPOSURE, -1);      // not working
cap->set(CV_CAP_PROP_AUTO_EXPOSURE, 1);  // not working, exposure stays fixed
cap->set(CV_CAP_PROP_AUTO_EXPOSURE, 0);  // not working, exposure stays fixed
cap->set(CV_CAP_PROP_AUTO_EXPOSURE, -1); // not working, exposure stays fixed

Any idea?