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直入正题。编译protobuf的android版本我们使用的环境如下

                CMake: 3.6
                NDK: r16b
                Protobuf: v3.5.1
                OS : Mac os

首先我们下载protobuf的代码https://github.com/google/protobuf/releases 直接下载cpp平台的就可以了。

1 首先进入到cmake目录下，创建一个文件夹 build-armeabi-v7a

2 然后我们在根目录下（protobuf的顶层目录）添加一个android.sh，代码如下

cd cmake && cd build-armeabi-v7a

# Step 3. Generate Makefile with CMake.
# -Dprotobuf_BUILD_SHARED_LIBS=ON           By default is static library (*.a file). I want a
#                                           shared library (*.so file).
# -DCMAKE_INSTALL_PREFIX                    Because it's a cross-compiled library. You probably
#                                           want to install the header files and shared library
#                                           in specific folder rather than default /usr/local 
#                                           directory.
# -DANDROID_STL=c++_shared                  For the library using C++11, link to C++11 runtime.
# -DANDROID_LINKER_FLAGS="-landroid -llog"  For the library using functions of libandroid.so
#                                           and liblog.so.
# -DANDROID_CPP_FEATURES="rtti exceptions"  Most ppl use exception and runtime-type-information 
#                                           features in their C++ projects.
#
# Debug Tips:
# Add -LAH to see variables.
#/Users/yxwang/Library/Android/sdk/cmake/3.6.4111459/bin/cmake \
<your-path-of>/cmake \
    -Dprotobuf_BUILD_SHARED_LIBS=OFF \
    -Dprotobuf_BUILD_STATIC_LIBS=ON \
    -DCMAKE_VERBOSE_MAKEFILE=ON \
    -Dprotobuf_BUILD_TEST=OFF \
    -Dprotobuf_BUILD_EXAMPLES=OFF \
    -DCMAKE_TOOLCHAIN_FILE=/Users/yxwang/Library/Android/sdk/ndk-bundle/build/cmake/android.toolchain.cmake \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX=<install-path> \
    -DANDROID_NDK=<ndk-path> \
    -DANDROID_TOOLCHAIN=clang \
    -DANDROID_ABI=armeabi-v7a \
    -DANDROID_NATIVE_API_LEVEL=16 \
    -DANDROID_STL=c++_shared \
    -DANDROID_LINKER_FLAGS="-landroid -llog" \
    -DANDROID_CPP_FEATURES="rtti exceptions" \
    ..

# Step 4. Run Make with generated Makefile.
<your-path-of>/cmake --build .

# Step 5 (optional). Install the generated header files and shared library 
# to specific folder.
make install

PS:注意这里的android.toolchain.cmake的地址，并不是直接放在sdk/cmake/version/下的那个文件……使用这个文件会报错。可以在android studio中创建一个拥有c++的项目，然后编译一次，在.externalNativeBuild/cmake_build_command.txt中能够找到位置，直接拿来用就行。

另外这里生成的是.a的静态库，如果需要.so的动态库，可以吧上面protobuf_build_shared_libs这个编译选项设置为on

3. 在运行之前还需要修改原来的 cmake文件

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我这里只留下了 protobuf-lite的库，所以最后也只会生成这个库。如果需要libprotobuf.so库，可以把这部分也放出来。

不过libprotoc和protoc是无法使用ndk编译的，所以一定需要注释掉。

在项目中使用的时候可能会出现这样的提示

Error:FAILURE: Build failed with an exception.

* What went wrong:
.....
  FAILED: : && /Users/yxwang/Library/Android/sdk/ndk-bundle/toolchains/llvm/prebuilt/darwin-x86_64/bin/clang++  --target=aarch64-none-linux-android --gcc-toolchain=/Users/yxwang/Library/Android/sdk/ndk-bundle/toolchains/aarch64-linux-android-4.9/prebuilt/darwin-x86_64 --sysroot=/Users/yxwang/Library/Android/sdk/ndk-bundle/sysroot -fPIC -isystem /Users/yxwang/Library/Android/sdk/ndk-bundle/sysroot/usr/include/aarch64-linux-android -D__ANDROID_API__=21 -g -DANDROID -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -Wa,--noexecstack -Wformat -Werror=format-security -std=c++11 -frtti -fexceptions --std=c++1z -O0 -fno-limit-debug-info  -Wl,--exclude-libs,libgcc.a -Wl,--exclude-libs,libatomic.a --sysroot /Users/yxwang/Library/Android/sdk/ndk-bundle/platforms/android-21/arch-arm64 -Wl,--build-id -Wl,--warn-shared-textrel -Wl,--fatal-warnings -L/Users/yxwang/Library/Android/sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/arm64-v8a -Wl,--no-undefined -Wl,-z,noexecstack -Qunused-arguments -Wl,-z,relro -Wl,-z,now -shared -Wl,-soname,libTKATPROTOBUF.so -o ../../../../build/intermediates/cmake/debug/obj/arm64-v8a/libTKATPROTOBUF.so src/main/cpp/shared/tkat.protobuf/CMakeFiles/TKATPROTOBUF.dir/src/protobuf-handler.cpp.o src/main/cpp/shared/tkat.protobuf/CMakeFiles/TKATPROTOBUF.dir/src/protobuf-message-decorator.cpp.o src/main/cpp/shared/tkat.protobuf/CMakeFiles/TKATPROTOBUF.dir/src/tkat.dbf.sjs.pb.cc.o src/main/cpp/shared/tkat.protobuf/CMakeFiles/TKATPROTOBUF.dir/src/tkat.login.pb.cc.o src/main/cpp/shared/tkat.protobuf/CMakeFiles/TKATPROTOBUF.dir/src/tkat.pb.cc.o src/main/cpp/shared/tkat.protobuf/CMakeFiles/TKATPROTOBUF.dir/src/tkat.quote.pb.cc.o  ../../../../src/main/cpp/protobuf/arm64-v8a/lib/libprotobuf.a -latomic -lm "/Users/yxwang/Library/Android/sdk/ndk-bundle/sources/cxx-stl/llvm-libc++/libs/arm64-v8a/libc++.a" && :
  ../../../../src/main/cpp/protobuf/arm64-v8a/lib/libprotobuf.a(common.cc.o): In function `google::protobuf::internal::DefaultLogHandler(google::protobuf::LogLevel, char const*, int, std::__ndk1::basic_string<char, std::__ndk1::char_traits<char>, std::__ndk1::allocator<char> > const&)':
  /Users/yxwang/Desktop/protobuf-3.5.1/src/google/protobuf/stubs/common.cc:142: undefined reference to `__android_log_write'
  /Users/yxwang/Desktop/protobuf-3.5.1/src/google/protobuf/stubs/common.cc:150: undefined reference to `__android_log_write'
  clang++: error: linker command failed with exit code 1 (use -v to see invocation)
  ninja: build stopped: subcommand failed.


* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

* Get more help at https://help.gradle.org

BUILD FAILED in 22s

表示_android_log_write未定义，而是是报在静态库中的。

解决方案


find_library( # Defines the name of the path variable that stores the
                  # location of the NDK library.
                  log-lib

                  # Specifies the name of the NDK library that
                  # CMake needs to locate.
                  log)

target_link_libraries(TKATPROTOBUF PUBLIC ${PROTOBUF_LIBRARY} ${log-lib})

在使用Protobuf库的时候，同时添加log-lib库的链接。

Android跨平台编译 —— protobuf

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