How to specify -W4 (Visual Studio) in a Qt project?

Question

My environment:

• Windows 10, 64-bit
• Microsoft Visual Studio 2015
• Qt 5.6.2
• Qt Creator 4.8.1

I want to compile my C++ project with -W4 instead of the default -W3, so I added this line to my .pro file:

QMAKE_CXXFLAGS += -W4

But then, I get many of these warnings (one for each compilation unit, I suppose):

cl : Command line warning D9025 : overriding '/W4' with '/W3'

From the command line, I can see that the command line does include both -W3 and -W4 (in this order).

So, my question: How can I swap the order of -W3 and -W4 (so -W4 would take precedence over -W3)?

Note that this did not work: I tried to modify Qt's configuration file C:\Qt\5.6.2\msvc2015_64\mkspecs\common\msvc-desktop.conf, by changing the value of variable QMAKE_CFLAGS_WARN_ON from -W3 to -W4, and not adding -W4 to QMAKE_CXXFLAGS in my .pro file, but that caused many (thousands) of warnings being generated by libraries. I also tried to append -W4 to QMAKE_CXXFLAGS_WARN_ON (instead of QMAKE_CXXFLAGS) in my .pro file, with the same result (thousands of warnings from libraries).

Also note that if I add -Wall (instead of -W4) to QMAKE_CXXFLAGS, then:

• I do not get similar command line warnings (although -Wall is followed by -W3 on the command line)
• I still get many warnings from libraries, but considerably less than with -W3 changed to -W4 in msvc-desktop.conf (or with -W4 appended to QMAKE_CXXFLAGS_WARN_ON in my .pro file).

I use qmake (through Qt Creator), so any solutions that would require editing the generated Visual Studio project files would be unacceptable.

Answer 1

The change to your project file appends the warning setting to the existing variable, which is predefined:

QMAKE_CXXFLAGS += -W4

You could either prepend the variable, or actually replace the existing warning variable setting with your own:

QMAKE_CXXFLAGS ~= s/-W3/-W4