Conditional compilation

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187

answers:

Conditional compilation

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

+3 A:

Usually something like CXXFLAGS+=-DSAVE_DATA

Richard Pennington 2009-12-05 00:59:23

+3 A:

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

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

Dirk Eddelbuettel 2009-12-05 00:59:38

Note that modifying CXXFLAGS is how you pass options to the C++ compiler in make.

Roger Pate 2009-12-05 01:20:17

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 2009-12-05 01:47:34

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 2009-12-05 02:21:03

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 2009-12-05 02:26:50