I've been following this tutorial trying to get working QT cross-compilation from my PC to a Raspberry Pi Zero W.
It is failing on Step 5 ("Install a bunch of development files").
Running sudo apt-get build-dep qt4-x11 results in this:
builddeps:qt4-x11 : Depends: debhelper (>= 9) but it is not installable
Depends: default-libmysqlclient-dev ...
...
(similar "depends" error continues about 20 lines)
...
E: Unable to correct problems, you have held broken packages.
A similar situation results when running sudo apt-get build-dep libqt5gui5.
Running sudo apt-get install libudev-dev reports E: Unable to locate package libudev-dev, and fails.
This is my /etc/apt/sources.list file:
deb http://mirrordetector.raspbian.org/raspbian stretch main contrib non-free rpi
deb-src http://archive.raspbian.org/raspbian stretch main contrib non-free rpi
sudo apt updatebefore trying to install packages? The repo source also seems to indicate that you either did not install an RPF Raspbian image or it has not been updated/upgraded for a long timeapt update. It seems to work fine except for a line at the end:E: The repository ... does not have a Release file.I originally installed Raspbian from raspberrypi.org/downloads/raspbian a few days ago, though I have edited thesources.listfile from its original state, since this same error was occurring with the original sources.though I have edited the sources.list file from its original state,that's what I suspected. Current default is pointing to raspbian.raspberrypi.org. I would restore the default and try update / upgrade again. If that results in an error then update your question with that. No use in trying to install anything if you get an error during 'update'