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I'm trying to add the newest version of openCV to my iOS project, but when I compile, I get about 30 link errors:

Example:

Undefined symbols for architecture i386:
"cv::merge(std::vector<cv::Mat, std::allocator<cv::Mat> > const&, cv::_OutputArray const&)", referenced from:

I added the OpenCV framework, along with all the other required frameworks, in a dummy app with a simple video capture (following the tutorial in the link), and it worked perfectly.

I'm not sure why it could have worked so smoothly in one place, but not in the other. My only thought is that I ame compiling for different architectures between the two apps, but I think for both I'm aiming at armv7 and armv7s.

Any idea on what could be causing link errors?

Jason
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  • Your question is not clear - first you say you are getting link errors, then you go on to say that the framework worked. Are you using the same version of the framework in each case, and are your projects both new projects? – foundry Jan 06 '13 at 20:44
  • There are two projects: one just a simple test one I through together, another with my full application. It works in the test project, but when I follow the same steps, there are link errors. I think there are different architectures supported in each but I can't figure out which/how/etc. – Jason Jan 06 '13 at 21:18

1 Answers1

13

Check this: (assuming you are using LLVM compiler)

Target > Build Settings > Apple LLVM Compiler 4.1 - language > C++ Standard Library
try selecting 

libstdc++ (GNU C++ standard library)`

then try switch to 

libc++ (LLVM C++ standard library with C++11 support)

libstdc++ seems to work for older builds of openCV, libc++ correct for newer builds. If you have it set wrong (either way) you will see these kinds of errors.

If that isn't the cause, open the build setting side by side in each project and check every setting...

I have been battling through this recently - see my question here, answers here and github sample here. The github project includes opencv framework compiled from current source a few days ago. Right now I am putting together a multi-target sample that links to a different version of the framework if compiling under 10.6/XCode4.2 or 10.7/XCode4.4+. [On github here]

update

As @mikewoz requested, you may need to run current openCV with libstdc++ to remain compatible with other frameworks. It is possible to make a current build with libstdc++ compatibility. For details see my answer to Mike's question here:

OpenCV 2.4.3+ with libstdc++ for iOS?

Community
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foundry
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  • Thank you so much! You must made my afternoon! It was set to "Compiler Default" so I changed it to "libc++ (LLVM C++ standard library with C++11 support)" and it worked! – Jason Jan 06 '13 at 21:33
  • Agree, for current openCV 2.4.4, libc++ is the right choice, and it's not the default. – jimpic Mar 01 '13 at 18:30
  • What if we need to use libstdc++ because of other 3rd party libraries that are also in a project? Is there a way that we can build the latest OpenCV without libc++ / C++11 support? and fall back onto libstdc++? – mikewoz Apr 06 '13 at 20:32
  • @mikewoz - I haven't tried, but in `ios/cmake/Modules/Platform/iOS.cmake` you can change `libc++` to `libstdc++` in "`set (CMAKE_CXX_FLAGS "`". If you have any luck, perhaps you could add a comment back here. – foundry Apr 06 '13 at 23:19
  • Worked for me. Switched from default compiler to LLVM C++ standard with C++11 support as you specified. Thanks much! – ninehundreds Feb 14 '14 at 17:50