Compiling for iOS with CMake - c++

Question

I've compiled a C++ static library by using CMake as my building tool and I want to link it to my iOS app.
I created a simple 'Empty' application in Xcode and linked my library called libengine.a to it.
I tried to compile my iOS project and the linker gave me this warning:
ignoring file /Users/.../build/engine/libengine.a,
file was built for archive which is not the architecture being linked (i386):
/Users/.../build/engine/libengine.a
As I understand it, I need to compile my library for ARM processors. The problem is I don't know how.
I think CMake really lacks good tutorials.
Anyways, my CMake scripts are attached below.
Any help would be greatly appreciated.
Thanks, Tal.
Here is my main CMake script:
cmake_minimum_required(VERSION 2.8)
project(movie-night)
if (DEFINED PLATFORM)
include(toolchains/ios.cmake)
endif()
add_definitions(-Wall)
set(DEBUG)
if (DEFINED DEBUG)
add_definitions(-g)
endif()
if (DEFINED RELEASE)
add_definitions(-O3)
endif()
add_subdirectory(engine)
add_subdirectory(ui)
add_subdirectory(test)
Here is my toolchains/ios.cmake file:
set(CMAKE_SYSTEM_NAME Darwin)
set(CMAKE_SYSTEM_PROCESSOR arm)

Answer 1

Just use this toolchain file: http://code.google.com/p/ios-cmake/ and use it as
cmake -DCMAKE_TOOLCHAIN_FILE=path_to_your_toolchain_file
Then, in CMakeLists.txt:
SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -arch armv7")
SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -arch armv7")

Answer 2

By following cmake-toolchains documentation I did like below:
cmake -G Xcode -B build \
-DCMAKE_SYSTEM_NAME=iOS \
-DCMAKE_Swift_COMPILER_FORCED=true \
-DCMAKE_OSX_DEPLOYMENT_TARGET=11.0
Note: That assignment CMAKE_OSX_DEPLOYMENT_TARGET=11.0 is not a mistake when targeting iOS.

Answer 3

I've been using an updated version of the iOS CMake toolchain for quite a while: https://github.com/leetal/ios-cmake
This creates an Xcode project which you can drag into an existing iOS project if necessary.
I wrote a blog post with more details: https://blog.tomtasche.at/2019/05/how-to-include-cmake-project-in-xcode.html

Answer 4

There is a second version of iOS.cmake located at:
https://ceres-solver.googlesource.com
Note: You may find that both versions of iOS.cmake will only build x86 versions of your project. CMake now sets CMAKE_OSX_SYSROOT to the (latest) Mac OS X SDK available on your system. You can fix this by modifying your copy of iOS.cmake to always set CMAKE_OSX_SYSROOT. You can do this by commenting out a couple of lines your copy of iOS.cmake:
# -- Under CMake 3.4.2, CMAKE_OSX_SYSROOT is automatically defined to point to the latest Mac OS X SDK. --
# -- So, the iOS SDK is never found. Grab the correct CMAKE_OS_SYSROOT and ignore any prior setting. --
# If user did not specify the SDK root to use, then query xcodebuild for it.
# if (NOT CMAKE_OSX_SYSROOT)
execute_process(COMMAND xcodebuild -version -sdk ${XCODE_IOS_PLATFORM} Path
OUTPUT_VARIABLE CMAKE_OSX_SYSROOT
ERROR_QUIET
OUTPUT_STRIP_TRAILING_WHITESPACE)
message (STATUS "Using SDK: ${CMAKE_OSX_SYSROOT} for platform: ${IOS_PLATFORM}")
message (STATUS "be sure the previous line points to the correct SDK")
# endif ( )