What Does This Line Mean? Local_export_c_includes

Very simple question, hoping for a very simple answer. I've been looking at a lot of people's android.mk files and have noticed this line. I had no documentation on it within my

Solution 1:

The following explanation for the LOCAL_EXPORT_* variables in ANDROID-MK.html in the docs folder of the r6 NDK:

LOCAL_EXPORT_CFLAGS Define this variable to record a set of C/C++ compiler flags that will be added to the LOCAL_CFLAGS definition of any other module that uses this one with LOCAL_STATIC_LIBRARIES or LOCAL_SHARED_LIBRARIES.

For example, consider the module 'foo' with the following definition:

include$(CLEAR_VARS)
   LOCAL_MODULE := foo
   LOCAL_SRC_FILES := foo/foo.c
   LOCAL_EXPORT_CFLAGS := -DFOO=1
   include$(BUILD_STATIC_LIBRARY)

And another module, named 'bar' that depends on it as:

   include $(CLEAR_VARS)
   LOCAL_MODULE := bar
   LOCAL_SRC_FILES := bar.c
   LOCAL_CFLAGS := -DBAR=2
   LOCAL_STATIC_LIBRARIES := foo
   include $(BUILD_SHARED_LIBRARY)

Then, the flags '-DFOO=1 -DBAR=2' will be passed to the compiler when building bar.c

Exported flags are prepended to your module's LOCAL_CFLAGS so you can easily override them. They are also transitive: if 'zoo' depends on 'bar' which depends on 'foo', then 'zoo' will also inherit all flags exported by 'foo'.

Finally, exported flags are not used when building the module that exports them. In the above example, -DFOO=1 would not be passed to the compiler when building foo/foo.c.

LOCAL_EXPORT_CPPFLAGS Same as LOCAL_EXPORT_CFLAGS, but for C++ flags only.

LOCAL_EXPORT_C_INCLUDES Same as LOCAL_EXPORT_CFLAGS, but for C include paths. This can be useful if 'bar.c' wants to include headers that are provided by module 'foo'.