What qmake variable is used for Objective-C compilation flags?

Question

QMAKE_CXXFLAGS are applied when compiling .cpp files, but not applied to .mm files. Which flag should I use instead?

Answer 1

Those flags belong in QMAKE_OBJECTIVE_CFLAGS (not QMAKE_OBJECTIVE_CXXFLAGS).

The flags used in precompiled header generation go into QMAKE_OBJCXXFLAGS_PRECOMPILE,

Objective-C compilation is handled by qtbase/mkspecs/features/mac/objective_c.prf. An objective_c compiler is defined on-the-fly when Objective C/C++ sources are present. You can glean other details there.

The precompilation flags are handled by the Unix makefile generator: qtbase/qmake/generators/unix/unixmake.cpp and unixmake2.cpp.

I offer no comment as to the consistency of those variable names and their locus of implementation. Don't shoot the messenger.