C++ Makefile, Library Folders

Tags: C++ , Make   (2015-08-29)

Earlier, we allowed each library to have individual compilation flags. Here, we will re-implement this feature in a more flexible way, and allow libraries to specify multiple directories that contain source code.

First, we modify library_src_files gets modified to accept a second parameter, containing the directories that should be searched for source files.

library_src_files = $(foreach src_dir,$(2),$(call find_in_dir,$(1)/$(src_dir),$(CPP_EXT) $(C_EXT)))
library_o_files   = $(call o_file_name,$(call library_src_files,$(1),$(2)))
library_os_files   = $(addsuffix s,$(call library_o_files,$(1),$(2)))

The next part is a large chunk, but we’ll break it down into smaller pieces afterward. This defines a function, calls it, then evaluates the result multiple times.

define library_commands

    ifneq ($$(BUILD_STATIC),0)
       STATIC_LIBRARY := $$(call STATIC_LIBRARY_NAME,$(1))
    else
       STATIC_LIBRARY :=
    endif

    ifneq ($$(BUILD_SHARED),0)
       SHARED_LIBRARY := $$(call SHARED_LIBRARY_NAME,$(1))
    else
       SHARED_LIBRARY :=
    endif

    LIBRARY = $$(SHARED_LIBRARY) $$(STATIC_LIBRARY)
    LIBRARY_SRC_DIRS = src

    -include $(1)/Makefile.inc

    build/$$(BUILD)/$$(call SHARED_LIBRARY_NAME,$(1)): $$(call library_os_files,$(1),$$(LIBRARY_SRC_DIRS))
	mkdir -p $(@D)
	$$(CXX) $$(ALL_LDFLAGS) $$^ -shared $$(SHARED_LDLIBS) -o $$@

    build/$$(BUILD)/$$(call STATIC_LIBRARY_NAME,$(1)): $$(call library_o_files,$(1),$$(LIBRARY_SRC_DIRS))
	mkdir -p $(@D)
	$$(AR) rcs $$@ $$^
endef

$(foreach lib,$(LIBRARY_FOLDERS),$(eval $(call library_commands,$(lib))))

First, we define three variables, STATIC_LIBRARY, SHARED_LIBRARY, and LIBRARY. These point to the library that is currently being made. Then, library-specific variables can be defined as target-specific variables on these targets.

$(LIBRARY): ALL_CPPFLAGS += -DMY_DEFINE

We also define a default value for LIBRARY_SRC_DIRS, which can be overridden by the include file.

Finally, we define targets for the library to be generated. Here, we expand the calls to library_o_files to determine which files need to be included. This uses LIBRARY_SRC_DIRS, searching for src files only in the directories specified.

The full makefile can be found on github.