Building OpenCV as a static library leads to thousands of undefined references - c++

Question

I am working on Ubuntu 18.04 and i want to build OpenCV(4.1.0) as static lib and create a sample program. Building OpenCV works flawlessly but i get thousands of errors when i run the test application.
Building OpenCV:
configure cmake:
cmake -D CMAKE_BUILD_TYPE=Release -D
OPENCV_GENERATE_PKGCONFIG=ON -D
BUILD_SHARED_LIBS=OFF -D
OPENCV_EXTRA_MODULES_PATH=../../opencv_contrib-4.1.0/modules
-D CMAKE_INSTALL_PREFIX=/usr/local/opencv
..
build:
make -j8
install:
sudo make install
pkg-config setup:
sudo cp unix-install/opencv4.pc /usr/lib/x86_64-linux-gnu/pkgconfig/
Sample Program
#include <stdio.h>
#include <opencv2/opencv.hpp>
int main( int argc, char** argv )
{
cv::Mat testmat;
printf("Test\n");
return 0;
}
build:
g++ TestApp.cpp -o TestApp `pkg-config --cflags --libs opencv4`
I get these errors: Full Console.log
/usr/local/opencv/lib/libopencv_highgui.a(window_gtk.cpp.o): In function `cvImageWidget_class_init(void*, void*)&apos;: window_gtk.cpp:
.text._ZL24cvImageWidget_class_initPvS_+0xa): undefined reference to `gtk_widget_get_type&apos; window_gtk.cpp:
.text._ZL24cvImageWidget_class_initPvS_+0x15): undefined reference to `g_type_class_peek&apos; window_gtk.cpp:
.text._ZL24cvImageWidget_class_initPvS_+0x20): undefined reference to `g_type_check_class_cast&apos; /usr/local/opencv/lib/libopencv_highgui.a(window_gtk.cpp.o): In function `icvOnTrackbar(_GtkWidget*, void*)&apos;: window_gtk.cpp:
.text._ZL13icvOnTrackbarP10_GtkWidgetPv+0xd): undefined reference to `gtk_range_get_type&apos; window_gtk.cpp:
.text._ZL13icvOnTrackbarP10_GtkWidgetPv+0x18): undefined reference to `g_type_check_instance_cast&apos; window_gtk.cpp:
.text._ZL13icvOnTrackbarP10_GtkWidgetPv+0x20): undefined reference to `gtk_range_get_value&apos; /usr/local/opencv/lib/libopencv_highgui.a(window_gtk.cpp.o): In function `std::_Sp_counted_ptr_inplace&lt;CvWindow, std::allocator&lt;CvWindow&gt;, (__gnu_cxx::_Lock_policy)2&gt;::_M_dispose()&apos;: window_gtk.cpp:
.text._ZNSt23_Sp_counted_ptr_inplaceI8CvWindowSaIS0_ELN9__gnu_cxx12_Lock_policyE2EE10_M_disposeEv[_ZNSt23_Sp_counted_ptr_inplaceI8CvWindowSaIS0_ELN9__gnu_cxx12_Lock_policyE2EE10_M_disposeEv]+0x12): undefined reference to `gtk_widget_destroy&apos; /usr/local/opencv/lib/libopencv_highgui.a(window_gtk.cpp.o): In function `icvWindowThreadLoop(void*)&apos;: window_gtk.cpp:
.text._ZL19icvWindowThreadLoopPv+0x41): undefined reference to `gtk_main_iteration_do&apos; window_gtk.cpp:
.text._ZL19icvWindowThreadLoopPv+0x53): undefined reference to `g_usleep&apos; window_gtk.cpp:(.text._ZL19icvWindowThreadLoopPv+0x58): undefined reference to `g_thread_yield&apos; window_gtk.cpp:
.text._ZL19icvWindowThreadLoopPv+0x113): undefined reference to `gtk_main_iteration_do&apos; window_gtk.cpp:
.text._ZL19icvWindowThreadLoopPv+0x11d): undefined reference to `g_usleep&apos; window_gtk.cpp:(.text._ZL19icvWindowThreadLoopPv+0x122): undefined reference to `g_thread_yield&apos; /usr/local/opencv/lib/libopencv_highgui.a(window_gtk.cpp.o): In function `cvImageWidget_size_request(_GtkWidget*, _GtkRequisition*)&apos;: window_gtk.cpp:
(.text._ZL26cvImageWidget_size_requestP10_GtkWidgetP15_GtkRequisition+0x19): undefined reference to `gtk_widget_get_type&apos; window_gtk.cpp:
.text._ZL26cvImageWidget_size_requestP10_GtkWidgetP15_GtkRequisition+0x47): undefined reference to `g_type_register_static_simple&apos; window_gtk.cpp:
.text._ZL26cvImageWidget_size_requestP10_GtkWidgetP15_GtkRequisition+0x5b): undefined reference to `g_type_check_instance_cast&apos; /usr/local/opencv/lib/libopencv_highgui.a(window_gtk.cpp.o): In function `cvImageWidget_set_size(_GtkWidget*, int, int)&apos;: window_gtk.cpp:
.text._ZL22cvImageWidget_set_sizeP10_GtkWidgetii+0x19): undefined reference to `gtk_widget_get_type&apos; window_gtk.cpp:.text._ZL22cvImageWidget_set_sizeP10_GtkWidgetii+0x47): undefined reference to `g_type_register_static_simple&apos;
I would be thankful for any help.
Testing a fix:
The obvious answer is that OpenCV can not generate a correct .pc file in static mod. But i dont think thats the problem. To verify i built OpenCV3.2.0(the .pc file generates correctly in 3.2.0 as far as i know) and installed the perbuilt version with "sudo apt-get install libopencv-dev". The prebuilt worked but i got the same errors with the self-built version. I diffchecked both files and they were pretty much the same.
DiffCheck: diff
opencv.pc(pre-build): pre
opencv.pc(self-build): self
build-output(opencv): opencvbuild
build-output(testapp): testappbuild

Answer 1

I fixed it
My build command was missing the --static flag.
g++ TestApp.cpp -o TestApp `pkg-config --cflags --static --libs opencv4`
Now it can build my test application with OpenCV3.2.0 with no problems but I get this error when i use OpenCV4.1.0.
/usr/bin/ld: cannot find -lgflags_shared
I dont think I need this lib so i fixed this by removing -lgflags_shared from the opencv.pc file. Doing it manually works but using the command line is more convenient.
sed -i 's/-lgflags_shared //g' unix-install/opencv4.pc