Undefined symbols for architecture x86_64 Using QT with Opencv - qt

Question

I am using QT's IDE with OpenCV. The code works fine in Xcode but when I copy them to QT for GUI design, it doesn't work at all. I searched like crazy...
Here is the error message:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ -c -pipe -g -gdwarf-2 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.8.sdk -mmacosx-version-min=10.9 -Wall -W -fPIE -DQT_CORE_LIB -I../../../../Qt/5.2.1/clang_64/mkspecs/macx-clang -I../Hello -I/usr/local/include -I../../../../Qt/5.2.1/clang_64/lib/QtCore.framework/Versions/5/Headers -I. -I. -F/Users/Chenxi/Qt/5.2.1/clang_64/lib -o main.o ../Hello/main.cpp
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ -headerpad_max_install_names -Wl,-syslibroot,/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.8.sdk -mmacosx-version-min=10.9 -o Hello main.o -F/Users/Chenxi/Qt/5.2.1/clang_64/lib -L/usr/local/lib -lopencv_core -lopencv_imgproc -lopencv_highgui -lopencv_objdetect -lopencv_calib3d -framework QtCore
Undefined symbols for architecture x86_64:
"cv::imread(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, int)", referenced from:
_main in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [Hello] Error 1
main.cpp:
So it should be the link error with opencv I think.
#include <QCoreApplication>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv/cv.h>
#include <iostream>
using namespace std;
using namespace cv;
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
cout<<"hello world"<<endl;
Mat test(10,10,CV_8UC1);
cout<<test.cols<<endl;
Mat test1 = imread("/Users/master/desktop/FYP/GUI/Demo_db/neg_1.png");
return a.exec();
}
.pro file:
QT += core
QT -= gui
TARGET = Hello
CONFIG += console
CONFIG -= app_bundle
TEMPLATE = app
INCLUDEPATH += /usr/local/include
LIBS += -L/usr/local/lib \
-lopencv_core \
-lopencv_imgproc \
-lopencv_highgui \
-lopencv_objdetect \
-lopencv_calib3d
SOURCES += main.cpp
I have tried this answer but it doesn't work for me:
QMAKE_MACOSX_DEPLOYMENT_TARGET = 10.6 to 10.9
Could anyone help me? Thanks.

Answer 1

I think you will need to change from the default gnu C++ std implementation to the following by passing it to your compiler, which is presumably clang:
-stdlib=libc++
In short, do not mix gcc and clang if you do that because unfortunately they are not 100% abi compatible, sadly. You could check which one the libopencv was built with:
otool -L libopencv-version.dylib