I'm writing a build script for a Qt application. The script first calls qmake on the .pro file and then runs make CXXFLAGS=-DSWVERSION=xxxx.

The problem with this is that it overwrites the CXXFLAGS already defined in the Makefile. Currently, the only method I know to solve this problem is to edit the Makefile and change this:

CXXFLAGS      = <flags>

To this:

CXXFLAGS       = <flags>

I was hoping there would be a simpler solution. Is there any way I can simply append to CXXFLAGS from the command line WITHOUT rewriting the Makefile?

Alternatively, my real problem is defining SWVERSION at build-time (because it is dependent on the build timestamp). Do you know of a better way to define this at runtime instead of passing it to CXXFLAGS?

CodePudding user response：

The change you suggest won't work anyway: a value set on the command line completely overrides the value set in the makefile, even if the value is appended to with =. You could do this and it would work:

override CXXFLAGS  = <flags>

However, the way it's normally done is that the makefile provides variables which are reserved specifically for users to override on the command line. For example in automake-generated makefiles, the common variables like CXXFLAGS, CFLAGS, etc. are reserved for users to set via the command line or environment, and the internal makefile flags are put into a different variable, like AM_CFLAGS. Then the recipes to compile objects uses both variable, like $(CC) $(AM_CFLAGS) $(CFLAGS) ...

I don't know anything about qt so I can't say whether they have a similar set of reserved makefile variables but you might check the qt docs, or your generated makefile recipes, to see.

CodePudding user response：

For anyone reading this in the future, the solution I found was to call qmake <project file> DEFINES ="SWVERSION=xxxx". Hope someone finds this helpful.