Linker errors after upgrading Xcode to 4.5.2 and OpenCV to 2.4.3 - ios

Question

My project was working just fine until this morning. I was using xcode 4.3, and an older version of OpenCV (I'm not sure about the exact version). OSX was already 10.7.x, but not 10.7.5
Today, after upgrading OSX to 10.7.5, xcode to 4.5.2, and downloading OpenCV 2.4.3, I am getting the following linker errors when trying to build the project:
Undefined symbols for architecture armv7:
"_OBJC_CLASS_$_ALAssetsLibrary", referenced from:
objc-class-ref in opencv2(cap_ios_video_camera.o)
"cv::FeatureDetector::create(std::string const&)", referenced from:
-[ImageAnalyzer detectBlobs:] in ImageAnalyzer.o
"cv::FeatureDetector::detect(cv::Mat const&, std::vector >&, cv::Mat const&) const", referenced from:
-[ImageAnalyzer detectBlobs:] in ImageAnalyzer.o
ld: symbol(s) not found for architecture armv7
clang: error: linker command failed with exit code 1 (use -v to see invocation)
In order to use the new opencv framework I removed the reference to the old framework, and referenced the project to the official prebuilt opencv2.framework downloaded from here.
I also removed the reference to libz.dylib, and added a reference to libc++.dylib instead.
Last step was to update the prefix file to the new framework. The relevant part in the prefix file now looks like this:
#ifdef __cplusplus
#import <opencv2/opencv.hpp>
#endif
It all narrowed down to these 4 linker errors I can't seem to get rid of. I tried using libstdc++.dylib, but I am getting even more errors. I also tried building OpenCV myself as explained here, but I am still getting the same errors as the prebuilt framework.
What did I miss? Is there anything else I need to change in my project?
UPDATE:
As seen here, setting the "C++ Standard Library" to "libc++ (LLVM C++ standard libray with C++ 11 support" yielded only one error:
clang: error: invalid deployment target for -stdlib=libc++ (requires iOS 5.0 or later)
Changing the deployment target to iOS 5 finally got my project to run again.
Does this mean OpenCV 2.4.3 doesn't work on iOS versions older than 5?

Answer 1

steps to compile and run c++ opencv 2.4.4 on mac os x lion 10.7.5 with cmake 2.8.10 and xcode 4.6.1
Having the right tools
download opencv-unix from http://sourceforge.net/projects/opencvlibrary/files/ and untar it wherever
download cmake .dmg from http://www.cmake.org/cmake/resources/software.html and install it
i am assuming you have xcode 4.6 on os x lion which includes the ios sdk 6.1
go to xcode preferences to download and install the Command Line Tools so you have g++ etc.
Use cmake to compile opencv
go to the extracted opencv folder
create a build directory
mkdir build
cd build
cmake -D WITH_TBB=OFF -D BUILD_NEW_PYTHON_SUPPORT=OFF -D BUILD_FAT_JAVA_LIB=OFF -D BUILD_TBB=OFF -D BUILD_EXAMPLES=ON -D CMAKE_CXX_COMPILER=g++ CMAKE_CC_COMPILER=gcc -D CMAKE_OSX_ARCHITECTURES=x86_64 -D BUILD_opencv_java=OFF -G "Unix Makefiles" ..
make -j8
sudo make install
from the build folder, go to bin/ and run one of the tests
./opencv_test_stitching
Create your own c++ opencv xcode project
fire up xcode and create a new xcode project
select Command Line Tool for the type of project under os x
open your project's build settings
under Architectures, set Architecture to 64-bit intel. also set Valid Architectures to x86_64
under Build Options, set Compiler for C/C++ to Default Compiler
under Search Paths, set Header Search Paths to /usr/local/include
also under Search Paths, set Library Search Paths to /usr/local/lib
under Apple LLVM compiler 4.2 - Language set C++ Standard Library to libstd++ (For OpenCV 2.4.6, Xcode 5, LLVM 5.0, and 10.8.5, set both language dialect and std library to "Compiler Default" instead of "libstd++")
Add the compiled opencv libraries to your project
go the the Build Phases tab next to Build Settings tab you were in
inside Link Binary With Libraries, click on the + sign and choose Add Other
hit the front slash / on your keyboard and enter /usr/local/lib
hit enter and select the libraries you want to use in your project
make sure you always select libopencv_core.2.4.4.dylib
hit enter and you will see the selected dylibs under your project
write some code
first lets organize the files, right click on your project blueprint icon and select New Group
name the new group opencv or whatever
drag the dylibs and drop them in that group
open main.cpp
copy code from any of the sample tests that came with opencv and paste it here
make sure all the required dylibs are added, for example, if you copied the opencv_test_stitching.cpp code into main.cpp, you will need to add the following libraries in the previous steps
libopencv_core.2.4.4.dylib
libopencv_highgui.2.4.4.dylib
libopencv_stitching.2.4.4.dylib
Cheers.

Answer 2

It seems that your project is missing the framework AssetsLibrary.
Select the top node in the project navigator. (The project and targets page with the build settings appears.)
Select the target.
Select Summary.
Scroll down to Linked Frameworks and Libraries.
Click the Plus icon at the end of the table and select AssetsLibrary.framework.
Click Add.
Then try to build it again.

Answer 3

Since I can't seem to get an answer regarding the versions (neither here nor at the OpenCV Q&A site), I'm going to post this as an answer, as it at least solved the issue. This is described here.
In your project's Build Settings, go down to the section Apple LLVM compiler 4.1-Language.
There:
Set C++ Language Dialect to Compiler Default
Set C++ Standard Libray to libc++ (LLVM C++ standard libray with C++ 11 support
After doing the above, I stopped getting those linker errors, and only got one error instead, which stated that only iOS 5 and above is supported. Changing the Deployment Target to 5.0 in the project summery did the trick.
On a final note, I'm still not sure what it means, regarding OpenCV 2.4.3's compatibility with iOS versions older than 5.

Answer 4

clang: error: invalid deployment target for -stdlib=libc++ (requires iOS 5.0 or later) to remove this error.
GoTo BuildSettings. Set c++ standard library to compiler default. The
error will get removed surely.

Answer 5

Just to get this into the postings somewhere in case someone else runs into the same thing. If you follow all the great advice aboutsetting the proper c++ library to link against for building an iOS app BUT still get the link errors for undefined symbols make sure your code files are set to compile as c++! That is rename your .m to .mm and .h to .hpp. It's the little things...

Answer 6

Instead of using terminal commands given in the opencv installation guide in official website, use the following commands to build opencv from terminal. Worked for me.
cd OpenCV-2.3.1
mkdir build
cd build
cmake -G "Unix Makefiles" ..
make
sudo make install

Answer 7

Go Xcode/General/Linked Frameworks and Libraries
Press "+" button
type: AssetsLibrary
Select "AssetsLibrary.framework" and import it
Done
Good luck!