title: Opencv Undefined symbols for architecture cv:imwrite Mac osX high Sierra
body: <p>I downloaded GCC and opencv(3.4.1_2) in my Mac OS X high Sierra(10.13.3) through homebrew.</p>
  
  <pre><code>$ g++ --version
  g++-7 (Homebrew GCC 7.3.0_1) 7.3.0
  </code></pre>
  
  <p>In my "opencvtest.cpp", <strong>cv::imwrite</strong> was seen as <strong>undefined symbols for architecture</strong> but other functions such as cv::imread, cv::namedWindow worked perfectly.</p>
  
  <pre><code>#include "opencv2/highgui/highgui.hpp"
  #include "opencv2/imgcodecs.hpp"
  #include &lt;iostream&gt;
  
  using namespace cv;
  int main( int argc, char** argv ) {
     Mat img = imread( argv[1], -1 );
     if( img.empty() ) return -1;
     namedWindow( "Example1", cv::WINDOW_AUTOSIZE );
     imshow( "Example1", img );
     imwrite("Example1.jpg", img);         //&lt;-- error
     waitKey( 0 );
     destroyWindow( "Example1" );
  }
  </code></pre>
  
  <p>Makefile was written as:</p>
  
  <pre><code>CC = g++
  CFLAGS = -g -Wall -std=c++11
  OPENCV = `pkg-config --cflags --libs opencv`
  
  test: opencvtest.o
     $(CC) -o $@ opencvtest.o $(CFLAGS) $(OPENCV)
  
  opencvtest.o: opencvtest.cpp
     $(CC) -c opencvtest.cpp $(CFLAGS) $(OPENCV)
  </code></pre>
  
  <p>Compilation using g++ in terminal yielded:</p>
  
  <pre><code>In file included from /usr/local/Cellar/opencv/3.4.1_2/include/opencv2/core.hpp:54:0,
                   from /usr/local/Cellar/opencv/3.4.1_2/include/opencv2/highgui.hpp:46,
                   from /usr/local/Cellar/opencv/3.4.1_2/include/opencv2/highgui/highgui.hpp:48,
                   from opencvtest.cpp:2:
  /usr/local/Cellar/opencv/3.4.1_2/include/opencv2/core/base.hpp:381:35: warning:unknown option after '#pragma GCC diagnostic' kind [-Wpragmas]
   #   pragma GCC diagnostic ignored "-Winvalid-noreturn"
                                     ^~~~~~~~~~~~~~~~~~~~
  g++ -o test opencvtest.o -g -Wall -std=c++11 `pkg-config --cflags --libs opencv`
  Undefined symbols for architecture x86_64:
    "cv::imwrite(cv::String const&amp;, cv::_InputArray const&amp;, std::vector&lt;int, std::allocator&lt;int&gt; &gt; const&amp;)", referenced from:
        _main in opencvtest.o
  ld: symbol(s) not found for architecture x86_64
  collect2: error: ld returned 1 exit status
  make: *** [test] Error 1
  </code></pre>
  
  <p>If I commented the problematic <code>imwrite("Example1.jpg", img);</code>, the program worked perfectly and the image can be shown. I had reinstalled opencv3 for many times and this problem seemed to be unsolvable. Can any clever people tell me what should I do next?</p>
  
  <p><strong>Edit</strong>:Here is my opencv profile. It said that the default C++ compiler was clang++ but not g++-7.</p>
  
  <pre><code>$opencv_version -v
  
  General configuration for OpenCV 3.4.1 =====================================
    Version control:               unknown
  
    Extra modules:
      Location (extra):            /tmp/opencv-20180307-60086-ryy1b3/opencv-3.4.1/opencv_contrib/modules
      Version control (extra):     unknown
  
    Platform:
      Timestamp:                   2018-03-07T08:15:55Z
      Host:                        Darwin 17.3.0 x86_64
      CMake:                       3.10.2
      CMake generator:             Unix Makefiles
      CMake build tool:            /usr/local/Homebrew/Library/Homebrew/shims/super/gmake
      Configuration:               Release
  
    CPU/HW features:
      Baseline:                    SSE SSE2 SSE3
        requested:                 SSE3
        disabled:                  SSE4_1 SSE4_2 AVX AVX2
      Dispatched code generation:  SSE4_1 SSE4_2 FP16 AVX AVX2 AVX512_SKX
        requested:                 SSE4_1 SSE4_2 AVX FP16 AVX2 AVX512_SKX
        SSE4_1 (3 files):          + SSSE3 SSE4_1
        SSE4_2 (1 files):          + SSSE3 SSE4_1 POPCNT SSE4_2
        FP16 (1 files):            + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 AVX
        AVX (5 files):             + SSSE3 SSE4_1 POPCNT SSE4_2 AVX
        AVX2 (9 files):            + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 FMA3 AVX AVX2
        AVX512_SKX (1 files):      + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 FMA3 AVX AVX2 AVX_512F AVX512_SKX
  
    C/C++:
      Built as dynamic libs?:      YES
      C++11:                       YES
      C++ Compiler:                /usr/local/Homebrew/Library/Homebrew/shims/super/clang++  (ver 9.0.0.9000039)
      C++ flags (Release):         -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -Wno-long-long -Qunused-arguments -Wno-semicolon-before-method-body -ffunction-sections -fdata-sections  -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -DNDEBUG  -DNDEBUG
      C++ flags (Debug):           -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -Wno-long-long -Qunused-arguments -Wno-semicolon-before-method-body -ffunction-sections -fdata-sections  -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -g  -O0 -DDEBUG -D_DEBUG
      C Compiler:                  /usr/local/Homebrew/Library/Homebrew/shims/super/clang
      C flags (Release):           -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -Wno-long-long -Qunused-arguments -Wno-semicolon-before-method-body -ffunction-sections -fdata-sections  -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -DNDEBUG  -DNDEBUG
      C flags (Debug):             -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -Wno-long-long -Qunused-arguments -Wno-semicolon-before-method-body -ffunction-sections -fdata-sections  -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -g  -O0 -DDEBUG -D_DEBUG
      Linker flags (Release):      
      Linker flags (Debug):        
      ccache:                      NO
      Precompiled headers:         NO
      Extra dependencies:          /usr/local/lib/libtbb.dylib
      3rdparty dependencies:
  
    OpenCV modules:
      To be built:                 aruco bgsegm bioinspired calib3d ccalib core datasets dnn dnn_objdetect dpm face features2d flann fuzzy hfs highgui img_hash imgcodecs imgproc java_bindings_generator line_descriptor ml objdetect optflow phase_unwrapping photo plot python2 python3 python_bindings_generator reg rgbd saliency shape stereo stitching structured_light superres surface_matching text tracking video videoio videostab xfeatures2d ximgproc xobjdetect xphoto
      Disabled:                    js world
      Disabled by dependency:      -
      Unavailable:                 cnn_3dobj cudaarithm cudabgsegm cudacodec cudafeatures2d cudafilters cudaimgproc cudalegacy cudaobjdetect cudaoptflow cudastereo cudawarping cudev cvv dnn_modern freetype hdf java matlab ovis sfm ts viz
      Applications:                apps
      Documentation:               NO
      Non-free algorithms:         YES
  
    GUI: 
      Cocoa:                       YES
  
    Media I/O: 
      ZLib:                        /usr/lib/libz.dylib (ver 1.2.11)
      JPEG:                        build (ver 90)
      WEBP:                        build (ver encoder: 0x020e)
      PNG:                         /usr/local/lib/libpng.dylib (ver 1.6.34)
      TIFF:                        /usr/local/lib/libtiff.dylib (ver 42 / 4.0.9)
      OpenEXR:                     /usr/local/lib/libImath.dylib /usr/local/lib/libIlmImf.dylib /usr/local/lib/libIex.dylib /usr/local/lib/libHalf.dylib /usr/local/lib/libIlmThread.dylib (ver 2.2.0)
  
    Video I/O:
      FFMPEG:                      YES
        avcodec:                   YES (ver 57.107.100)
        avformat:                  YES (ver 57.83.100)
        avutil:                    YES (ver 55.78.100)
        swscale:                   YES (ver 4.8.100)
        avresample:                YES (ver 3.7.0)
      AVFoundation:                YES
  
    Parallel framework:            TBB (ver 2018.0 interface 10002)
  
    Trace:                         YES (with Intel ITT)
  
    Other third-party libraries:
      Intel IPP:                   2017.0.3 [2017.0.3]
             at:                   /tmp/opencv-20180307-60086-ryy1b3/opencv-3.4.1/build/3rdparty/ippicv/ippicv_mac
      Intel IPP IW:                sources (2017.0.3)
                at:                /tmp/opencv-20180307-60086-ryy1b3/opencv-3.4.1/build/3rdparty/ippicv/ippiw_mac
      Lapack:                      YES (/System/Library/Frameworks/Accelerate.framework /System/Library/Frameworks/Accelerate.framework)
      Eigen:                       YES (ver 3.3.4)
      Custom HAL:                  NO
      Protobuf:                    build (3.5.1)
  
    OpenCL:                        YES (no extra features)
      Include path:                NO
      Link libraries:              -framework OpenCL
  
    Python 2:
      Interpreter:                 /usr/local/opt/python@2/libexec/bin/python (ver 2.7.14)
      Libraries:                   /usr/local/Cellar/python@2/2.7.14_1/Frameworks/Python.framework/Versions/2.7/lib/libpython2.7.dylib (ver 2.7.14)
      numpy:                       /usr/local/lib/python2.7/site-packages/numpy/core/include (ver 1.14.1)
      packages path:               lib/python2.7/site-packages
  
    Python 3:
      Interpreter:                 /usr/local/opt/python/bin/python3 (ver 3.6.4)
      Libraries:                   /usr/local/opt/python/Frameworks/Python.framework/Versions/3.6/lib/python3.6/config-3.6m-darwin/libpython3.6.dylib (ver 3.6.4)
      numpy:                       /usr/local/lib/python3.6/site-packages/numpy/core/include (ver 1.14.1)
      packages path:               lib/python3.6/site-packages
  
    Python (for build):            /usr/local/opt/python@2/libexec/bin/python
  
    Java:                          
      ant:                         NO
      JNI:                         /Library/Java/JavaVirtualMachines/jdk-9.0.1.jdk/Contents/Home/include /Library/Java/JavaVirtualMachines/jdk-9.0.1.jdk/Contents/Home/include/darwin /Library/Java/JavaVirtualMachines/jdk-9.0.1.jdk/Contents/Home/include
      Java wrappers:               NO
      Java tests:                  NO
  
    Matlab:                        NO
  
    Install to:                    /usr/local/Cellar/opencv/3.4.1_2
  -----------------------------------------------------------------
  </code></pre>
  
  <p>Thus one only used <strong>clang++</strong> instead of <strong>g++</strong> with or without <code>CFLAG = -g</code> and compilation worked well. I wondered if one can change opencv default compiler from clang++ to g++?</p>