android - 这条线是什么意思？ LOCAL_EXPORT_C_INCLUDES

Question

非常简单的问题，希望得到一个非常简单的答案。我一直在查看很多人的 android.mk 文件并注意到这一行。我的 NDK 文档中没有关于它的文档(至少 find . -name "*.txt"| xargs grep "LOCAL_EXPORT_C_INCLUDES" 什么也没找到)。这是我读过的关于它的唯一文档...超出我的理解范围...

第 2 部分:我的假设是否正确，即我需要这一行才能将预构建的共享库与另一个模块一起使用？谢谢伙计们(和姑娘们)

III. Exporting headers for prebuilt libraries:

The example above was called 'naive' because, in practice, the code in foo-user.c is going to depend on specific declarations that are normally found in a header file distributed with the prebuilt library (e.g. "foo.h").

In other words, foo-user.c is going to have a line like:

include < foo.h >

And you need to provide the header and its include path to the compiler when building the foo-user module. A simple way to deal with that is to use exports in the prebuilt module definition. For example, assuming that a file "foo.h" is located under the 'include' directory relative to the prebuilt module, we can write:

`include $(CLEAR_VARS)

LOCAL_MODULE := foo-prebuilt

LOCAL_SRC_FILES := libfoo.so

LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/include

include $(PREBUILT_SHARED_LIBRARY)`

The LOCAL_EXPORT_C_INCLUDES definition here ensures that any module that depends on the prebuilt one will have its LOCAL_C_INCLUDES automatically prepended with the path to the prebuilt's include directory, and will thus be able to find headers inside that.

网址:http://www.srombauts.fr/android-ndk-r5b/docs/PREBUILTS.html

Answer 1

下面对ANDROID-MK.html中的LOCAL_EXPORT_*变量进行解释在 r6 NDK 的文档文件夹中:

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'.