How to Compile a Static Library Using the Android Ndk

How to compile a static library using the Android NDK?

As I understand it, the correct method is to use ndk-build and not invoking the compiler directly.

In Android.mk you need to specify a module for each static library you want to compile, and then specify that your shared library should use it.

Example of a modified Android.mk file of the hello-jni sample project:

LOCAL_PATH := $(call my-dir)

# Define vars for library that will be build statically.
include $(CLEAR_VARS)
LOCAL_MODULE := <module_name>
LOCAL_C_INCLUDES := <header_files_path>
LOCAL_SRC_FILES :=  <list_of_src_files>

# Optional compiler flags.
LOCAL_LDLIBS   = -lz -lm
LOCAL_CFLAGS   = -Wall -pedantic -std=c99 -g

include $(BUILD_STATIC_LIBRARY)

# First lib, which will be built statically.
include $(CLEAR_VARS)
LOCAL_MODULE := hello-jni
LOCAL_STATIC_LIBRARIES := <module_name>
LOCAL_C_INCLUDES := <header_files_path>
LOCAL_SRC_FILES := hello-jni.c

include $(BUILD_SHARED_LIBRARY)

If you want control over which modules to compile when you run ndk-build you can create create a Application.mk file (in the same directory as Android.mk) and list all the modules as in the following example:

APP_MODULES := <module_name_1> <module_name_2> ... <module_name_n>

Android NDK: building static library with other static libraries

NDK has the command you need, it's called LOCAL_EXPORT_STATIC_LIBRARIES.

include $(CLEAR_VARS)
LOCAL_EXPORT_STATIC_LIBRARIES := a-ssl a-crypto
LOCAL_C_INCLUDES += $(PATH_TO_PROJECT)/vendor/android-openssl/openssl/include
LOCAL_MODULE := project-alib
LOCAL_SRC_FILES := ../../source.c
include $(BUILD_STATIC_LIBRARY)

You could also inherit the openssl includes path from a-ssl. FInally, to clean this up a bit more, consider changing the order of modules in your Android.mk:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_EXPORT_STATIC_LIBRARIES := a-ssl a-crypto
LOCAL_MODULE := project-alib
LOCAL_SRC_FILES := ../../source.c
include $(BUILD_STATIC_LIBRARY)

LOCAL_PATH := $(PATH_TO_PROJECT)/vendor/android-openssl

include $(CLEAR_VARS)
LOCAL_MODULE := a-ssl
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/openssl/include
LOCAL_SRC_FILES := $(LOCAL_PATH)/prebuilt/$(TARGET_ARCH_ABI)/libcrypto.a
include $(PREBUILT_STATIC_LIBRARY)

include $(CLEAR_VARS)
LOCAL_MODULE := a-crypto
LOCAL_SRC_FILES := $(LOCAL_PATH)/prebuilt/$(TARGET_ARCH_ABI)/libssl.a
include $(PREBUILT_STATIC_LIBRARY)

Android, NDK, building static library

You should be able to use ar (arm-linux-androideabi-ar from the appropriate NDK toolchain) to achieve this:

arm-linux-androideabi-ar -xv lib1.a 
arm-linux-androideabi-ar -xv lib2.a 
arm-linux-androideabi-ar -xv lib3.a 
arm-linux-androideabi-ar -rc libmegalib.a *.o

Build static library with asset_manager using NDK r10e

When you build a static library, you don't need to satisfy the external references, but if somebody uses your library, they must link libandroid.so. You can put this in documentation of your library.

If you provide an Android.mk with it, you can set LOCAL_EXPORT_LDLIBS = -landroid. BTW, you can also set LOCAL_EXPORT_INCLUDES to the directory with public headers for your library.

At any rate, NDK 10 is obsolete. I strongly recommend to move to the current release (unless you desperately need support for android-3).

Build and use static library in Android NDK

I'm guessing C++ name mangling is problem here. Your lodepng.c file provides _lodepng_decode32 symbol (as it is compiled as C code), but your main.cpp file expects something like _lodepng_decode32$asdaASd symbol (because it is compiled as C++ code).

You should rename lodepng.c to lodepng.cpp.

Or you need to put #include "lodepng.h" in your main.cpp file inside extern "C" { ... } block.

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