【原+转】用CMake代替makefile进行跨平台交叉编译

　　在开始介绍如何使用CMake编译跨平台的静态库之前，先讲讲我在没有使用CMake之前所趟过的坑。因为很多开源的程序，比如png，都是自带编译脚本的。我们可以使用下列脚本来进行编译：

./configure  --prefix=/xxx/xx --enable-static=YES
make
make install

　　相信手动在类Unix系统上面编译过开源程序的同学对上面的命令肯定非常熟悉。更悲惨的是，有些开源库是不提供configure配置文件的，只有一个Makefile或者Makefile.gcc。我的体会是，Makefile是一个很复杂的东西，没有一定的积累我们是看不懂的，更别说去修改它了。而本文的CMake可以更傻瓜更简单地达到我们的目的，你不需要理会复杂的makefile语法。Just follow me!

　　 如果不配置编译器和一些编译、链接参数，这样的操作，最后编译出来的静态库只能在本系统上面被链接使用。比如你在mac上面运行上面的命令，编译出来的静态库就只能给mac程序链接使用。如果在Linux上面运行上述命令，则也只能给Linux上面的程序所链接使用。如果我们想要在Mac上面编译出ios和android的静态库，就必须要用到交叉编译。

　　要进行交叉编译，一般来说要指定目标编译平台的编译器，通常是指定一个CC环境变量，根据编译的是c库还是c++库，要分别指定C_flags和CXX_flag，当然还需要指定c/c++和系统sdk的头文件包含路径。总之，非常之繁琐。

为什么要使用CMake

　　为什么我们不使用autoconf？为什么我们不使用QMake,JAM,ANT呢？具体原因大家可以参考我在本文最后的参考链接里面的《Mastering CMake》一书的第一章。我自己使用CMake的感受就是：我原来编写bash，配置configure参数，读各个开源库的INSTALL文件(因为不同库的configure参数有差别)，配置各种编译flag，头文件包含等。最后3天时间，折腾了png和jepg两个库的编译。当然，中间我还写了android和linux的编译脚本。而换用CMake以后，我2天时间编译完了Box2D,spine和Chipmunk的编译。并且配置脚本相当简单，添加新的库，基本上只是拷贝脚本，修改一两个参数即可。有了CMake，编译跨平台静态库和生成跨平台可执行程序So Easy！

　　

编写CMakeLists.txt

　　编写一个静态库的CMake配置文件过程如下：（这里我以Box2D为例）

1、指定头文件和源文件

include_directories(
${CMAKE_CURRENT_SOURCE_DIR}
)

file(GLOB_RECURSE box2d_source_files "${CMAKE_CURRENT_SOURCE_DIR}/Box2D/*.cpp")

　　我的CMakeLists.txt和Box2D的文件结构关系如下图所示：

# This file is based off of the Platform/Darwin.cmake and Platform/UnixPaths.cmake
# files which are included with CMake 2.8.4
# It has been altered for iOS development

# Options:
#
# IOS_PLATFORM = OS (default) or SIMULATOR
#   This decides if SDKS will be selected from the iPhoneOS.platform or iPhoneSimulator.platform folders
#   OS - the default, used to build for iPhone and iPad physical devices, which have an arm arch.
#   SIMULATOR - used to build for the Simulator platforms, which have an x86 arch.
#
# CMAKE_IOS_DEVELOPER_ROOT = automatic(default) or /path/to/platform/Developer folder
#   By default this location is automatcially chosen based on the IOS_PLATFORM value above.
#   If set manually, it will override the default location and force the user of a particular Developer Platform
#
# CMAKE_IOS_SDK_ROOT = automatic(default) or /path/to/platform/Developer/SDKs/SDK folder
#   By default this location is automatcially chosen based on the CMAKE_IOS_DEVELOPER_ROOT value.
#   In this case it will always be the most up-to-date SDK found in the CMAKE_IOS_DEVELOPER_ROOT path.
#   If set manually, this will force the use of a specific SDK version

# Standard settings
set (CMAKE_SYSTEM_NAME Darwin)
set (CMAKE_SYSTEM_VERSION 1 )
set (UNIX True)
set (APPLE True)
set (IOS True)

# Force the compilers to gcc for iOS
include (CMakeForceCompiler)
#CMAKE_FORCE_C_COMPILER (gcc gcc)
#CMAKE_FORCE_CXX_COMPILER (g++ g++)
CMAKE_FORCE_C_COMPILER ("/usr/bin/gcc" gcc)
CMAKE_FORCE_CXX_COMPILER ("/usr/bin/g++" g++)

# Skip the platform compiler checks for cross compiling
set (CMAKE_CXX_COMPILER_WORKS TRUE)
set (CMAKE_C_COMPILER_WORKS TRUE)

# All iOS/Darwin specific settings - some may be redundant
set (CMAKE_SHARED_LIBRARY_PREFIX "lib")
set (CMAKE_SHARED_LIBRARY_SUFFIX ".dylib")
set (CMAKE_SHARED_MODULE_PREFIX "lib")
set (CMAKE_SHARED_MODULE_SUFFIX ".so")
set (CMAKE_MODULE_EXISTS 1)
set (CMAKE_DL_LIBS "")

set (CMAKE_C_OSX_COMPATIBILITY_VERSION_FLAG "-compatibility_version ")
set (CMAKE_C_OSX_CURRENT_VERSION_FLAG "-current_version ")
set (CMAKE_CXX_OSX_COMPATIBILITY_VERSION_FLAG "${CMAKE_C_OSX_COMPATIBILITY_VERSION_FLAG}")
set (CMAKE_CXX_OSX_CURRENT_VERSION_FLAG "${CMAKE_C_OSX_CURRENT_VERSION_FLAG}")

# Hidden visibilty is required for cxx on iOS
set (CMAKE_C_FLAGS "")
set (CMAKE_CXX_FLAGS "-headerpad_max_install_names -fvisibility=hidden -fvisibility-inlines-hidden")

set (CMAKE_C_LINK_FLAGS "-Wl,-search_paths_first ${CMAKE_C_LINK_FLAGS}")
set (CMAKE_CXX_LINK_FLAGS "-Wl,-search_paths_first ${CMAKE_CXX_LINK_FLAGS}")

set (CMAKE_PLATFORM_HAS_INSTALLNAME 1)
set (CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS "-dynamiclib -headerpad_max_install_names")
set (CMAKE_SHARED_MODULE_CREATE_C_FLAGS "-bundle -headerpad_max_install_names")
set (CMAKE_SHARED_MODULE_LOADER_C_FLAG "-Wl,-bundle_loader,")
set (CMAKE_SHARED_MODULE_LOADER_CXX_FLAG "-Wl,-bundle_loader,")
set (CMAKE_FIND_LIBRARY_SUFFIXES ".dylib" ".so" ".a")

# hack: if a new cmake (which uses CMAKE_INSTALL_NAME_TOOL) runs on an old build tree
# (where install_name_tool was hardcoded) and where CMAKE_INSTALL_NAME_TOOL isn't in the cache
# and still cmake didn't fail in CMakeFindBinUtils.cmake (because it isn't rerun)
# hardcode CMAKE_INSTALL_NAME_TOOL here to install_name_tool, so it behaves as it did before, Alex
if (NOT DEFINED CMAKE_INSTALL_NAME_TOOL)
find_program(CMAKE_INSTALL_NAME_TOOL install_name_tool)
endif (NOT DEFINED CMAKE_INSTALL_NAME_TOOL)

# Setup iOS platform
if (NOT DEFINED IOS_PLATFORM)
set (IOS_PLATFORM "OS")
endif (NOT DEFINED IOS_PLATFORM)
set (IOS_PLATFORM ${IOS_PLATFORM} CACHE STRING "Type of iOS Platform")

# Check the platform selection and setup for developer root
if (${IOS_PLATFORM} STREQUAL "OS")
set (IOS_PLATFORM_LOCATION "iPhoneOS.platform")
elseif (${IOS_PLATFORM} STREQUAL "SIMULATOR")
set (IOS_PLATFORM_LOCATION "iPhoneSimulator.platform")
else (${IOS_PLATFORM} STREQUAL "OS")
message (FATAL_ERROR "Unsupported IOS_PLATFORM value selected. Please choose OS or SIMULATOR")
endif (${IOS_PLATFORM} STREQUAL "OS")

# Setup iOS developer location
if (NOT DEFINED CMAKE_IOS_DEVELOPER_ROOT)
set (CMAKE_IOS_DEVELOPER_ROOT "/Developer/Platforms/${IOS_PLATFORM_LOCATION}/Developer")
endif (NOT DEFINED CMAKE_IOS_DEVELOPER_ROOT)
set (CMAKE_IOS_DEVELOPER_ROOT ${CMAKE_IOS_DEVELOPER_ROOT} CACHE PATH "Location of iOS Platform")

# Find and use the most recent iOS sdk
if (NOT DEFINED CMAKE_IOS_SDK_ROOT)
file (GLOB _CMAKE_IOS_SDKS "${CMAKE_IOS_DEVELOPER_ROOT}/SDKs/*")
if (_CMAKE_IOS_SDKS)
list (SORT _CMAKE_IOS_SDKS)
list (REVERSE _CMAKE_IOS_SDKS)
list (GET _CMAKE_IOS_SDKS 0 CMAKE_IOS_SDK_ROOT)
else (_CMAKE_IOS_SDKS)
message (FATAL_ERROR "No iOS SDK's found in default seach path ${CMAKE_IOS_DEVELOPER_ROOT}. Manually set CMAKE_IOS_SDK_ROOT or install the iOS SDK.")
endif (_CMAKE_IOS_SDKS)
message (STATUS "Toolchain using default iOS SDK: ${CMAKE_IOS_SDK_ROOT}")
endif (NOT DEFINED CMAKE_IOS_SDK_ROOT)
set (CMAKE_IOS_SDK_ROOT ${CMAKE_IOS_SDK_ROOT} CACHE PATH "Location of the selected iOS SDK")

# Set the sysroot default to the most recent SDK
set (CMAKE_OSX_SYSROOT ${CMAKE_IOS_SDK_ROOT} CACHE PATH "Sysroot used for iOS support")

# set the architecture for iOS - using ARCHS_STANDARD_32_BIT sets armv6,armv7 and appears to be XCode's standard.
# The other value that works is ARCHS_UNIVERSAL_IPHONE_OS but that sets armv7 only
set (CMAKE_OSX_ARCHITECTURES "$(ARCHS_STANDARD_64_BIT)" CACHE string  "Build architecture for iOS")

# Set the find root to the iOS developer roots and to user defined paths
set (CMAKE_FIND_ROOT_PATH ${CMAKE_IOS_DEVELOPER_ROOT} ${CMAKE_IOS_SDK_ROOT} ${CMAKE_PREFIX_PATH} CACHE string  "iOS find search path root")

# default to searching for frameworks first
set (CMAKE_FIND_FRAMEWORK FIRST)

# set up the default search directories for frameworks
set (CMAKE_SYSTEM_FRAMEWORK_PATH
${CMAKE_IOS_SDK_ROOT}/System/Library/Frameworks
${CMAKE_IOS_SDK_ROOT}/System/Library/PrivateFrameworks
${CMAKE_IOS_SDK_ROOT}/Developer/Library/Frameworks
)

# only search the iOS sdks, not the remainder of the host filesystem
set (CMAKE_FIND_ROOT_PATH_MODE_PROGRAM ONLY)
set (CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set (CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

我的iOS_64.cmake
　　如果上面的操作都没错，就会顺利生成一个project.xcodeproject文件，打开后记得做下面几件事情：

1、设置Product->Scheme->Edit Scheme为release模式

2、其他设置如图：





设置完毕后，点击运行，就能生成.a静态库了。这时候，你可以使用下面的命令测试一下生成的静态库是否真的是iOS下的库。

打开terminal，cd到.a所在目录，假设静态库名字为libMyLib.a，输入： lipo -info libMyLib.a ，如果显示 Architectures in the fat file: lib7z_C++_938.a are: armv7 arm64 就说明操作无误了。然后，尽情享用你的静态库吧！

编译linux静态库（含64位和32位）

编译linux的静态库是非常简单的，只需要安装好cmake以后，运行以下命令即可:

cmake .
make

注意，如果是64位的系统，那么这样只能生成64位的静态库。想要编译出32位的静态库，则必须要先安装32位系统的编译工具链。

sudo apt-get install libx32gcc-4.8-dev
sudo apt-get install libc6-dev-i386
sudo apt-get install lib32stdc++6
sudo apt-get install g++-multilib

　　然后，只需要指定cxx_flags为-m32即可，对应的CMake的写法为：

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -m32")

　　最后用cmake生成makefile并make即可生成32位的静态库。

编译mac静态库

　　这个比较简单，直接

Xcode -GXcode

，然后用xcodebuild命令即可。

编译Andoird静态库

　　编译android库我们同样可以引入一个toolchain文件，这里我是从android-cmake里面下载的。 在使用这个toolchain文件之前，我们先要使用ndk自带的make-standalone-toolchain.sh脚本来生成对应平台的toolchain.这个脚本位于你的NDK的路径下面的buil/tools目录下。

　　比如要生成arm平台的toolchain，我们可以使用下列命令:

sh $ANDROID_NDK/build/tools/make-standalone-toolchain.sh --platform=android-$ANDROID_API_LEVEL --install-dir=./android-toolchain --system=darwin-x86_64 --ndk-dir=/Users/guanghui/AndroidDev/android-ndk-r9d/ --toolchain=arm-linux-androideabi-4.8

　　这里的

$ANDROID_NDK

为你的NDK的安装路径。这段命令可以生成arm的toolchain，最终可以编译出armeabi和armeabi-v7a静态库。 如果想生成x86的toolchain，指需要使用下列命令:

sh $ANDROID_NDK/build/tools/make-standalone-toolchain.sh --platform=android-$ANDROID_API_LEVEL --install-dir=./android-toolchain-x86 --system=darwin-x86_64 --ndk-dir=/Users/guanghui/AndroidDev/android-ndk-r9d/ --toolchain=x86-4.8

　　

export PATH=$PATH:./android-toolchain/bin
export ANDROID_STANDALONE_TOOLCHAIN=./android-toolchain
cmake -DCMAKE_TOOLCHAIN_FILE=../android.toolchain.cmake -DANDROID_ABI="armeabi" ..

　　

编译Win32，wp8和winrt静态库

这里直接使用cmake-gui生成对应的VS工程，然后再手动编译即可。

关于Box2D完整的跨平台编译脚本可以参考子龙山人Github

Reference:

cmake by example

mastering cmake pdf

Meta-configuration of C/C++ projects with CMake

Setting up Android standalone toolchain for CMake

cmake and the Android NDK

android-cmake

CMake for Andrioid

ios-cmake google code

以上内容除iOS部分比较多原创外，其他内容大部分转自子龙山人bolg。

##THAT IS ALL.

=======================================

原创文章，转载请注明 编程小翁@博客园，邮件zilin_weng@163.com，微信Jilon，欢迎各位与我在C/C++/Objective-C/机器视觉等领域展开交流!

=======================================