Conditional compilation

Question

How do I add conditional compilation to my makefile: say if I have a #ifdef SAVE_DATA in a cpp (.cc) file.

score 4 · Accepted Answer · answered Dec 05 '09 at 00:59

4

Usually something like CXXFLAGS+=-DSAVE_DATA

answered Dec 05 '09 at 00:59

score 3 · Answer 2 · answered Dec 05 '09 at 00:59

3

For gcc et al, you can use the -Dfoo flag to define foo:

g++ -DSAVE_DATA=1 -c foo.cpp

answered Dec 05 '09 at 00:59

Dirk Eddelbuettel

Note that modifying CXXFLAGS is how you pass options to the C++ compiler in make. – Dec 05 '09 at 01:20
Yes that is one of many possibilities, but you can also use it implicitly as argument to the command ultimately using as I did here. – Dirk Eddelbuettel Dec 05 '09 at 01:47
I tend to do both: if I define a custom rule for particular cpp files, I write it as `$(CXX) $(CPPFLAGS) $(CXXFLAGS) -special -flags -c -o $@ $<`. Or sometimes with the special flags before CXXFLAGS, it's kind of the same issue as !important in CSS. – Steve Jessop Dec 05 '09 at 02:21
Of course you can use target-specific variables, but in my experience they cause more confusion than they save. Maybe I should have stuck with them longer. – Steve Jessop Dec 05 '09 at 02:26

2 Answers2