Build (linker) error by building C++ function with third-party library (OpenCV) in Simulink C/C++ Code Block

Dear community,

I want to add custom C++ code in a Simulink s-function, which is working well outside of MATLAB/Simulink. Unfortunately I am stuck since days, because of a build error with error messages as below:

### 'SemSegONNX.cpp' created successfully
### 'SemSegONNX_wrapper.cpp' created successfully
C:\Users\usr\AppData\Local\Temp\mex_89125236923555_19680\tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.obj:tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.cpp:(.text+0x9b): undefined reference to `cv::Mat::zeros(cv::Size_, int)'
C:\Users\usr\AppData\Local\Temp\mex_89125236923555_19680\tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.obj:tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.cpp:(.text+0xc6): undefined reference to `cv::Mat::Mat()'
C:\Users\usr\AppData\Local\Temp\mex_89125236923555_19680\tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.obj:tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.cpp:(.text+0x126): undefined reference to `cv::Mat::~Mat()'
C:\Users\usr\AppData\Local\Temp\mex_89125236923555_19680\tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.obj:tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.cpp:(.text+0x12f): undefined reference to `cv::Mat::~Mat()'
C:\Users\usr\AppData\Local\Temp\mex_89125236923555_19680\tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.obj:tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.cpp:(.text+0x138): undefined reference to `cv::Mat::~Mat()'
C:\Users\usr\AppData\Local\Temp\mex_89125236923555_19680\tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.obj:tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.cpp:(.text+0x1fd): undefined reference to `cv::Mat::~Mat()'
C:\Users\usr\AppData\Local\Temp\mex_89125236923555_19680\tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.obj:tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.cpp:(.text+0x219): undefined reference to `cv::Mat::~Mat()'
C:\Users\usr\AppData\Local\Temp\mex_89125236923555_19680\tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.obj:tpf5dfed4c_669f_4bd9_a2e8_0609ae30efc6.cpp:(.text+0x225): more undefined references to `cv::Mat::~Mat()' follow collect2.exe: error: ld returned 1 exit status

I add the following C++ code in a "C/C++ Code Block" which should build:

#include <opencv2/opencv.hpp>
#include <vector>

void SemSegONNX_Start_wrapper(void)
{
    }

void SemSegONNX_Outputs_wrapper(const uint8_T *img, uint8_T *pred)
{
    // generate empty dummy image with shape 224x224
    cv::Mat image = cv::Mat::zeros(cv::Size(224,224),CV_8UC1);
    // only to generate vectorized outputs from image
    for (short i = 0; i < 224; ++i)
        for (short j = 0; j < 224; ++j)
            pred[i*224 + j] = img[i, j];
    }
        
void SemSegONNX_Terminate_wrapper(void)
{
    }

The shown code shows only a minimal example of the code I want to run, but the occurring errors are the same. It seems that there is a general problem. The compilation process runs well, but the linker cannot find the included library. Via the command line, I can compile the code successfully by:

g++ -Wall -o _foo.exe -Ipackages\onnxruntime-win-x64-1.12.0\include -ID:\opencv\build_mingw_x64\install\include -Lpackages\onnxruntime-win-x64-1.12.0\lib -LD:\opencv\build_mingw_x64\install\x64\mingw\bin _foo.cpp -lopencv_world470 -lonnxruntime

My understanding of the documentation of the generation of the mex-function is that that is only a wrapper build around the custom C++ code. So I am afraid the problem is a correct setup of the LIB_PATH, INC_PATH and ENTRY. The way I have done this as follows seems to be not correct.

LIB_PATH	D:\opencv\build_mingw_x64\install\x64\mingw\bin
INC_PATH	D:\opencv\build_mingw_x64\install\include
ENTRY		libopencv_world470.dll

All shown steps are done on a Windows 10, MinGW-W64 gcc 13.0.1, MATLAB Support for MinGW-w64 C/C++ Compiler v22.2.0

I am happy to get support in this field. Thanks in advance.

Best regards

Answer 1

[Rasmita]

Hi,

It is my understanding that, you are getting above mentioned build error when you add the custom C++ code that uses OpenCV in a Simulink s-function.

The error

undefined reference to `cv::Mat::__()'

may be due to some missing OpenCV libraries. Please search in the official website of OpenCV to get those libraries and link it.

Hope this helps!

Regards,

Rasmita

[greencactus]

Hello Rasmita,

Thanks for your answer. As described, the code is successfully compilable and executable outside of MATLAB. The library OpenCV is pre-compiled for my operating system and available via the set paths:

LIB_PATH D:\opencv\build_mingw_x64\install\x64\mingw\bin

INC_PATH D:\opencv\build_mingw_x64\install\include

ENTRY libopencv_world470.dll

Via the command line, I can compile the code with linker arguments:

g++ -Wall -o _foo.exe -ID:\opencv\build_mingw_x64\install\include -LD:\opencv\build_mingw_x64\install\x64\mingw\bin _foo.cpp -lopencv_world470

Only the linker of MATLAB's C++ s-function block cannot find the linked libraries. This behavior raises the error. Further, the file opencv_world470.dll is a dynamic library. It did not work with static *.lib files, either. I have the strong suspicion that some configuration of the C++ s-function block is wrong.

The main idea of the integration of C++ code is to refactor code from other projects. I know about the OpenCV interface from MATLAB. I do not need OpenCV at all, but it is representative for other third party C++ libraries. It would be very helpful if you could provide a minimal example of this block with included third party libraries.

Best regards