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POLinker errors after upgrading Xcode to 4.5.2 and OpenCV to 2.4.3
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copied!<p>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<br /> <br /> 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:<br /></p> <blockquote> <p>Undefined symbols for architecture armv7:<br /> "_OBJC_CLASS_$_ALAssetsLibrary", referenced from:<br /> objc-class-ref in opencv2(cap_ios_video_camera.o)<br /> "cv::FeatureDetector::create(std::string const&)", referenced from:<br /> -[ImageAnalyzer detectBlobs:] in ImageAnalyzer.o<br /> "cv::FeatureDetector::detect(cv::Mat const&, std::vector >&, cv::Mat const&) const", referenced from:<br /> -[ImageAnalyzer detectBlobs:] in ImageAnalyzer.o<br /> ld: symbol(s) not found for architecture armv7<br /> clang: error: linker command failed with exit code 1 (use -v to see invocation)</p> </blockquote> <p>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 <a href="http://sourceforge.net/projects/opencvlibrary/files/opencv-ios/2.4.3/opencv2.framework.zip/download" rel="noreferrer">here</a>.<br /> I also removed the reference to <strong>libz.dylib</strong>, and added a reference to <strong>libc++.dylib</strong> instead.<br /> Last step was to update the prefix file to the new framework. The relevant part in the prefix file now looks like this:<br /></p> <pre><code>#ifdef __cplusplus #import <opencv2/opencv.hpp> #endif </code></pre> <p>It all narrowed down to these 4 linker errors I can't seem to get rid of. I tried using <strong>libstdc++.dylib</strong>, but I am getting even more errors. I also tried building OpenCV myself as explained <a href="http://docs.opencv.org/trunk/doc/tutorials/introduction/ios_install/ios_install.html#ios-installation" rel="noreferrer">here</a>, but I am still getting the same errors as the prebuilt framework.<br /> <br /> What did I miss? Is there anything else I need to change in my project?<br /> <br /> <br /> UPDATE:<br /> As seen <a href="http://code.opencv.org/issues/2500" rel="noreferrer">here</a>, setting the "C++ Standard Library" to "libc++ (LLVM C++ standard libray with C++ 11 support" yielded only one error:<br /></p> <blockquote> <p>clang: error: invalid deployment target for -stdlib=libc++ (requires iOS 5.0 or later)</p> </blockquote> <p>Changing the deployment target to iOS 5 finally got my project to run again.<br /> Does this mean OpenCV 2.4.3 doesn't work on iOS versions older than 5?</p>

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