Android.mk 中变量含义

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LS_CPP = $(subst $(1)/,,$(wildcard $(1)/*.cpp))

LOCAL_SRC_FILES := $(call LS_CPP,$(LOCAL_PATH))

Android.mk 中变量含义：

• LOCAL_ variables: These are dedicated to individual module compilation and are defined in Android.mk files. 

• APP_ variables: These refer to application-wide options and are set in Application.mk. 

• NDK_ variables: These are mainly internal variables that usually refer to environment variables (for example, NDK_ROOT, NDK_APP_CFLAGS, or NDK_APP_CPPFLAGS). There are two notable exceptions: NDK_TOOLCHAIN_VERSION and NDK_ APPLICATION_MK. The latter can be passed to the NDK-Build in parameter to define a different Application.mk location. 

• PRIVATE_ prefixed variables: These are for NDK internal use only. 

 

LOCAL_PATH : To specify the root location of source files. Must be defined at the beginning of the Android.mk file before include $(CLEAR_VARS). 

LOCAL_SRC_FILES : To define the list of source files to compile, each separated by a space and relative to LOCAL_PATH. 

 

$(wildcard <pattern>) : Selects files and directory names according to a pattern. 

$(call <function>) : Allows evaluating a function or macro. One macro we have seen is my-dir, which returns the directory path of the last executed Makefile. This is why LOCAL_PATH := $(call my-dir) is systematically written at the beginning of each Android.mk file to save in the current Makefile directory. 

$(subst <from>,<replacement>,<string>) : Replaces each occurrence of a substring by another. The second one is more powerful because it allows using patterns (which must start with "%"). 

 

Custom functions can easily be written with the call directive. These functions look somewhat similar to recursively affected variables, except that the arguments can be defined: $(1) for first argument, $(2) for second argument, and so on. A call to a function can be performed in a single line, as shown in the following code:  

 my_function = $(<do_something> ${1} , ${2})
 $(call my_function, myparam)

 

APP_ABI : List of ABI (that is, "CPU architectures") supported by the application, separated by a space. Currently supported values are armeabi, armeabi-v7a, x86, mips, or all. Each module is recompiled once per ABI. So, the more ABI you support, the more time it will get to build. 

APP_STL : The C++ runtime to use. Possible values are system, gabi++_ static, gabi++_shared, stlport_static, stlport_ shared, gnustl_static, gnustl_shared, c++_static, and c++_shared. 

 

［参考文献］

Android NDK- Beginner's Guide - Second Edition

http://www.gnu.org/software/make/manual/make.html#Wildcard-Function

http://code.google.com/p/android-cmake.