Polymorphic type reference error during build

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System Information

This error occurs after make j*:

Scanning dependencies of target opencv_perf_imgproc
[ 37%] Building CXX object modules/imgproc/CMakeFiles/opencv_perf_imgproc.dir/perf/opencl/perf_3vs4.cpp.o
[ 37%] Building CXX object modules/cudaarithm/CMakeFiles/opencv_test_cudaarithm.dir/test/test_event.cpp.o
[ 37%] Building CXX object modules/cudaarithm/CMakeFiles/opencv_perf_cudaarithm.dir/perf/perf_element_operations.cpp.o
/home/ubuntu/opencv_contrib/modules/cudaarithm/test/test_event.cpp: In member function ‘void opencv_test::{anonymous}::AsyncEvent_Timing_Test::UnsafeTestBody()’:
/home/ubuntu/opencv_contrib/modules/cudaarithm/test/test_event.cpp:94:30: warning: catching polymorphic type ‘class cv::Exception’ by value [-Wcatch-value=]
   94 |         catch (cv::Exception ex) {

The warning message you're seeing is related to catching a polymorphic type by value instead of by reference. In C++, it's a good practice to catch exceptions by reference rather than by value to preserve the exception type information and to avoid object slicing.

Here's how you could fix this warning:

Change this line:
catch (cv::Exception ex) {

To:
catch (const cv::Exception& ex) {

Detailed description

By making this change, you're catching the exception by reference, which should eliminate the warning message. Now go back to your source code, find the file test_event.cpp, locate line 94, and make the suggested change. Save the file and re-compile your project. This should resolve the warning you were seeing.

Steps to reproduce

make j*

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues, forum.opencv.org, Stack Overflow, etc and have not found any solution
• I updated to the latest OpenCV version and the issue is still there
• There is reproducer code and related data files (videos, images, onnx, etc)