Question

What I have done is used some code from the tutorial based on the openCV framework.
From the EdgeDetectionSample.cpp file, I import the code.

Undefined symbols for architecture armv7:
“std::__1::basic_string, std::__1::allocator >::basic_string(std::__1::basic_string, std::__1::allocator > const&)”, referenced from:
cv::Exception::Exception(int, std::__1::basic_string, std::__1::allocator > const&, std::__1::basic_string, std::__1::allocator > const&, std::__1::basic_string, std::__1::allocator > const&, int) in opencv2(system.o)
cv::Exception::Exception(cv::Exception const&) in opencv2(system.o)
“std::__1::basic_string, std::__1::allocator >::~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::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)
cv::Mat::reserve(unsigned long) in opencv2(matrix.o)
…
“std::__1::basic_string, std::__1::allocator >::__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::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)
cv::Mat::reserve(unsigned long) in opencv2(matrix.o)
…
“std::_1::_vector_base_common::__throw_length_error() const”, referenced from:
std::_1::vector, std::__1::allocator > >::_append(unsigned long) in opencv2(matrix.o)
std::_1::vector, std::__1::allocator > >::_append(unsigned long) in opencv2(matrix.o)
std::_1::vector, std::__1::allocator > >::_append(unsigned long) in opencv2(matrix.o)
std::_1::vector, std::__1::allocator > >::_append(unsigned long) in opencv2(matrix.o)
std::_1::vector, std::__1::allocator > >::_append(unsigned long) in opencv2(matrix.o)
std::_1::vector, std::__1::allocator > >::_append(unsigned long) in opencv2(matrix.o)
std::_1::vector, std::__1::allocator > >::_append(unsigned long) in opencv2(matrix.o)
…
“std::__1::basic_string, std::__1::allocator >::operator=(std::__1::basic_string, std::__1::allocator > const&)”, referenced from:
cv::Exception::formatMessage() in opencv2(system.o)
ld: symbol(s) not found for architecture armv7
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Please Help me Out with this. I am not able to get read of those errors.

Answer 1

Your project is linked against libstd++ (GNU C++ standard library), but latest OpenCV was linked against libc++ (LLVM C++ standard library with C++ 11 support), so you have two ways to fix this:

1. Link you project against libc++
2. Rebuild OpenCV with libstd++.

To link your project with libc++, go to -> Build Settings -> find ‘C++ standard library’ row and select libc++ there.