Re: Creating an obj/ directory?

[Paul Smith]

On Thu, 2011-09-01 at 22:53 -0400, Jeffrey Walton wrote:
> Hi All,
> 
> I'm working with a project that has a modest tree structure. The *.o
> files are currently being placed next to their *.cpp counterparts. I
> would like to move them to an obj/ directory, maintaining the same
> structure.

> The problem is that our CPP build rule is getting in the way ('don't
> know how to make X'):
> 
> .cpp.o:
>       $(CXX) $(CXXFLAGS) $(INCLUDES) -fpic -c $< -o $@

You cannot use a suffix rule to define targets and source files in
different directories: they're just not powerful enough.  The stem of
the files must be character-for-character identical between them.

That's why GNU make supports pattern rules.  Rewrite your rule as:

  obj/%.o : %.cpp
          $(CXX) $(CXXFLAGS) $(INCLUDES) -fpic -c $< -o $@

Look up pattern rules in the GNU make manual for full details.

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