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Editorial Team
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Asked: 2026-06-16T13:42:57+00:00

My project was working just fine until this morning. I was using xcode 4.3,

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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?

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1 Answer

  1. Editorial Team

    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.

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