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Editorial Team
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Asked: 2026-06-15T06:34:19+00:00

I have been using a makefile that was fairly straightforward. I defined OBJS with

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I have been using a makefile that was fairly straightforward. I defined OBJS with a list of .cc files. I set up dependencies and include flags and appended all of those to $CXXFLAGS. It looks something like this:

SRCS = file1.cc file2.cc file3.cc
OBJS = $(SRCS:.cc=.o)
CXXFLAGS=some flags
CXXFLAGS+=some include dirs
$(mylib.so): $OBJS
    $CXX -shared -o $@ $^

mylib.so uses the CXXFLAGS (implicitly) and everything builds just fine.

I have recently had the need to have mylib_1.so and mylib_2.so, in addition to mylib.so. Each .so depend on all the same .cc files, but the compiler flags are all different (including include directories).

How do I get it so I can set the compiler flags based on the target .so? The problem that I have is that if I set CXXFLAGS more than once it gets overwritten. It’s almost like I need an if/else situation.

I tried doing something like setting three different flags, $CXXFLAGS1, $CXXFLAGS2, $CXXFLAGS3, and using those in the line

$(mylib1.so): $OBJS
    $CXX $(CXXFLAGS1) -shared -o $@ $^

but that does not work.

How do I accomplish what I am trying to do? Is it better to have 3 separate makefiles? I did find a way to get it to work. I can stop using $OBJS and spell out the flags explicitly for each source file but this seems like a horrible idea in terms of scaling to size.

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1 Answer

  1. Editorial Team

    Your CXXFLAGS1 in your example is only used at the stage of creating the .so file, not for compilation of the actual C++ sources (which is what you are trying to do, I assume).

    To achieve the above, consider making the Makefile invoke itself 3 times for 3 different targets and pass CXXFLAGS (with different values) as part of MAKEFLAGS or in the command line.

    Update: here’s an example

    all:  build-lib1 build-lib2 build-lib3

build-lib1:
    $(MAKE) $(MAKEFLAGS) CXXFLAGS="$(CXXFLAGS1)" lib1.so

build-lib2:
    $(MAKE) $(MAKEFLAGS) CXXFLAGS="$(CXXFLAGS2)" lib2.so

build-lib3:
    $(MAKE) $(MAKEFLAGS) CXXFLAGS="$(CXXFLAGS3)" lib3.so

$(lib1.so): $OBJS
    $(CXX) -shared -o $@ $^

etc...
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