Apple Mach-O linker and multiple "undefined symbols" error using OpenCV

Question

I am currently a real beginner in Objective C, and I am developing an app using the framework OpenCV.

I am following a tutorial, but while builing the project, I got several errors :

Undefined symbols for architecture i386:   "std::__1::basic_ostream<char, std::__1::char_traits<char> >::flush()", referenced from:       cv::gpu::error(char const*, char const*, int, char const*) in opencv2(gpumat.o)   "std::__1::basic_ostream<char, std::__1::char_traits<char> >::sentry::sentry(std::__1::basic_ostream<char, std::__1::char_traits<char> >&)", referenced from:       std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::operator<< <std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*) in opencv2(gpumat.o)   "std::__1::basic_ostream<char, std::__1::char_traits<char> >::sentry::~sentry()", referenced from:       std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::operator<< <std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*) in opencv2(gpumat.o)   "std::__1::basic_ostream<char, std::__1::char_traits<char> >::operator<<(int)", referenced from:       cv::gpu::error(char const*, char const*, int, char const*) in opencv2(gpumat.o)   "std::__1::cerr", referenced from:       cv::gpu::error(char const*, char const*, int, char const*) in opencv2(gpumat.o)   "std::__1::ios_base::__set_badbit_and_consider_rethrow()", referenced from:       std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::operator<< <std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*) in opencv2(gpumat.o)   "std::__1::ios_base::clear(unsigned int)", referenced from:       std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::operator<< <std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*) in opencv2(gpumat.o)   "std::__1::__vector_base_common<true>::__throw_length_error() const", referenced from:       __ZNSt3__16vectorImNS_9allocatorImEEE6assignIPmEENS_9enable_ifIXsr21__is_forward_iteratorIT_EE5valueEvE4typeES7_S7_ in opencv2(matrix.o)       std::__1::vector<unsigned long, std::__1::allocator<unsigned long> >::vector(unsigned long) in opencv2(matrix.o)       std::__1::vector<unsigned long, std::__1::allocator<unsigned long> >::__append(unsigned long) in opencv2(matrix.o)       std::__1::vector<cv::Vec<float, 2>, std::__1::allocator<cv::Vec<float, 2> > >::vector(unsigned long) in opencv2(matrix.o)       std::__1::vector<int, std::__1::allocator<int> >::vector(unsigned long) in opencv2(matrix.o)       std::__1::vector<cv::Vec<int, 128>, std::__1::allocator<cv::Vec<int, 128> > >::__append(unsigned long) in opencv2(matrix.o)       std::__1::vector<cv::Vec<int, 64>, std::__1::allocator<cv::Vec<int, 64> > >::__append(unsigned long) in opencv2(matrix.o)       ...   "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::__init(char const*, unsigned long)", referenced from:       cv::Mat::create(int, int const*, int) in opencv2(matrix.o)       __ZN2cvL7setSizeERNS_3MatEiPKiPKmb in opencv2(matrix.o)       cv::Mat::Mat(cv::Mat const&, cv::Range const&, cv::Range const&) in opencv2(matrix.o)       cv::Mat::Mat(cv::Mat const&, cv::Rect_<int> const&) in opencv2(matrix.o)       cv::Mat::Mat(cv::Mat const&, cv::Range const*) in opencv2(matrix.o)       cv::Mat::diag(int) const in opencv2(matrix.o)       cv::Mat::Mat(_IplImage const*, bool) in opencv2(matrix.o)       ...   "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::~basic_string()", referenced from:       cv::Mat::create(int, int const*, int) in opencv2(matrix.o)       __ZN2cvL7setSizeERNS_3MatEiPKiPKmb in opencv2(matrix.o)       cv::Mat::Mat(cv::Mat const&, cv::Range const&, cv::Range const&) in opencv2(matrix.o)       cv::Mat::Mat(cv::Mat const&, cv::Rect_<int> const&) in opencv2(matrix.o)       cv::Mat::Mat(cv::Mat const&, cv::Range const*) in opencv2(matrix.o)       cv::Mat::diag(int) const in opencv2(matrix.o)       cv::Mat::Mat(_IplImage const*, bool) in opencv2(matrix.o)       ...   "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::resize(unsigned long, char)", referenced from:       __ZL8icvCloseP13CvFileStoragePNSt3__112basic_stringIcNS1_11char_traitsIcEENS1_9allocatorIcEEEE in opencv2(persistence.o)   "std::__1::basic_string<wchar_t, std::__1::char_traits<wchar_t>, std::__1::allocator<wchar_t> >::__init(wchar_t const*, unsigned long)", referenced from:       cv::toUtf16(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) in opencv2(persistence.o)   "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::__init(char const*, unsigned long, unsigned long)", referenced from:       std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > std::__1::operator+<char, std::__1::char_traits<char>, std::__1::allocator<char> >(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, char const*) in opencv2(system.o)   "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::append(char const*)", referenced from:       cv::tempfile(char const*) in opencv2(system.o)   "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::append(char const*, unsigned long)", referenced from:       std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > std::__1::operator+<char, std::__1::char_traits<char>, std::__1::allocator<char> >(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, char const*) in opencv2(system.o)   "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::assign(char const*)", referenced from:       cv::tempfile(char const*) in opencv2(system.o)   "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::basic_string(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)", referenced from:       cv::Exception::Exception(int, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, int) in opencv2(system.o)       cv::tempfile(char const*) in opencv2(system.o)       cv::Exception::Exception(cv::Exception const&) in opencv2(system.o)       cv::operator<<(cv::FileStorage&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) in opencv2(persistence.o)   "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::operator=(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&)", referenced from:       cv::Exception::formatMessage() in opencv2(system.o)       cv::tempfile(char const*) in opencv2(system.o)       cv::operator<<(cv::FileStorage&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) in opencv2(persistence.o) ld: symbol(s) not found for architecture i386  clang: error: linker command failed with exit code 1 (use -v to see invocation) 

I am sure that the problem comes from the framework, but not the framework itself, but how it is link in the project, or...

I precise that I've linked it that way in the .pch file

 #import <Availability.h>  #ifndef __IPHONE_5_0 #warning "This project uses features only available in iOS SDK 5.0 and later." #endif  #ifdef __cplusplus #import <opencv2/opencv.hpp> #endif  #ifdef __OBJC__     #import <UIKit/UIKit.h>     #import <Foundation/Foundation.h> #endif 

Don't really know what to do..

EDIT : forgot to tell that I renamed my .m file to .mm and my .h file to .hh Is there anything else we need to do to get an objective C++ projet ?

Answer 1

Building on Cthutu's answer, to add libc++.dylib to your project:

1. Select your project (the blue file) in your project navigator (Command 1 if it's hidden)
2. Select your target
3. Go to Build Phases
4. Expand "Link Binary With Libraries"
5. Click the "+"
6. Type libc++.dylib in the search bar.
7. Select the libc++.dylib file and press "Add"

Answer 2

You're missing the standard C++ library. You need to link with it to get all the implementations for the STL classes you're getting errors for.

Add the libc++.dylib to your project.