Embedding files in an iOS app (C++/Qt/cmake) - c++

Question

In an iOS c++/Qt application, I need to ship a few files and to keep them in their directory structure.
For the Android version, we bundle a zip which we unzip on the target before creating the QApplication.
On iOS, it seems that CMake is not capable of bundling files in a tree:
https://cmake.org/cmake/help/latest/prop_tgt/RESOURCE.html#prop_tgt:RESOURCE
https://cmake.org/cmake/help/latest/prop_sf/MACOSX_PACKAGE_LOCATION.html
I am not sure if this is a limitation of cmake or if this is a global limitation on iOS.
From the docs about iOS bundles:
It uses a relatively flat structure with few extraneous directories in an effort to save disk space and simplify access to the files.
What would be the preferred approach?
Is there a solution to ship the files from CMake directly?
If not, how can I achieve this so that they are available before the QApplication is created?
The xcode command
Thanks to #Cy-4AH, I added the folder in Xcode and could get the command to do this:
CpResource _PATH_TO_DIRECTORY_ _APP_BUNDLE_DIRECTORY_/_RESOURCE_DIR_NAME_
cd /Users/denis/opt/qfield/ios/QField
export PATH="....."
builtin-copy -exclude .DS_Store -exclude CVS -exclude .svn -exclude .git -exclude .hg -strip-debug-symbols -strip-tool /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/strip -resolve-src-symlinks _PATH_TO_DIRECTORY_ _APP_BUNDLE_DIRECTORY_
But how can I create this from cmake? builtin-copyis an xcode command.
Simple system copy command
From an old (2008) discussion, we could use simple cp commands.
This works up to signing, but then I get an error unsealed contents present in the bundle root.
From this answer, it seems related that I cannot simply add folders in the resource directory. From the docs anatomy of framework bundles: Nonlocalized resources reside at the top level of the Resources directory

Answer 1

(Disclaimer: I'm not a CMake user, and there may be a more CMake-ey way to do this)
If you can set up post-build action, the following terminal script can efficiently sync files into your bundle from another location. I use it in my game engine because it only copies updated or new files upon subsequent builds, and preserves directory structure:
mkdir -p PATHTO/ORIGINFOLDERNAME
mkdir -p PATHTOBUILDFOLDER/PROJECTNAME.app/Contents/Resources/DESTINATIONFOLDERNAME
rsync -avu --delete --exclude=".*" PATHTO/ORIGINFOLDERNAME/ PATHTOBUILDFOLDER/PROJECTNAME.app/Contents/Resources/DESTINATIONFOLDERNAME
The mkdir commands are only to ensure that the folders are generated, if they were deleted.

Answer 2

So apparently the CMake method also works for directories.
target_sources(${QT_IOS_TARGET} PRIVATE ${_resource})
set_source_files_properties(${_resource} PROPERTIES MACOSX_PACKAGE_LOCATION Resources)
It will just be added at the root directory of the bundle and not within the Resources.

Answer 3

If the embedded file is not too big, you might consider :
in your source tree, generating a C++ file embedding that file as a constant array. For example, if your file contains just hello, world with a new line, you could have something like
/// file contents.cc
const char file_contents[] = "hello, world\n";
and at the beginning of your program (perhaps in your main function, before your QApplication) call a C++ function which writes such a file (perhaps in /tmp/).
in your build automation (e.g your Makefile or your qmake things), have something which generates the C++ contents.cc file from the genuine source
This is with a POSIX/Linux point of view, adapt my answer to your iOS.