Running OpenCV4.0.0 C++ function inside GoLang project

[StefanCepa]

What version of Go are you using (go version)?

$ go version 1.12

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/stefan/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/stefan/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS="-I/usr/local/include"
CGO_CXXFLAGS="--std=c++11"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-L/usr/local/lib -lopencv_core -lopencv_video -lopencv_videoio -lopencv_highgui"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build788193926=/tmp/go-build -gno-record-gcc-switches"

go env Output

$ go env

What did you do?

I am trying to run C++ function in GoLang project by wrapping it in C library first and then linking with my GoLang project. Details can be found on: https://stackoverflow.com/questions/55082336/running-opencv-4-0-0-c-function-in-golang

What did you expect to see?

I expected for my project to be built successfully.

What did you see instead?

command-line-arguments /tmp/go-build823465636/b001/_x002.o: In function "_cgo_dcf5d601f507_Cfunc_OpenVideo": /tmp/go-build/cgo-gcc-prolog:48: undefined reference to `OpenVideo' collect2: error: ld returned 1 exit status

And when running go build -x opencvTest.go I get the following:

WORK=/tmp/go-build568047770

mkdir -p $WORK/b001/

cd /home/stefan/Desktop/GoLang

CGO_LDFLAGS='"-L/usr/local/lib" "-lopencv_core" "-lopencv_video" "-lopencv_videoio" "-lopencv_highgui" "-L/usr/local/lib" "-lopencv_core" "-lopencv_video" "-lopencv_videoio" "-lopencv_highgui"' /usr/local/go/pkg/tool/linux_amd64/cgo -objdir $WORK/b001/ -importpath command-line-arguments -- -I/usr/local/include -I $WORK/b001/ -g -O2 ./opencvTest.go

cd $WORK

gcc -fno-caret-diagnostics -c -x c - || true

gcc -Qunused-arguments -c -x c - || true

gcc -fdebug-prefix-map=a=b -c -x c - || true

gcc -gno-record-gcc-switches -c -x c - || true

cd $WORK/b001

TERM='dumb' gcc -I /home/stefan/Desktop/GoLang -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches

-I/usr/local/include -I ./ -g -O2 -o ./_x001.o -c _cgo_export.c TERM='dumb' gcc -I /home/stefan/Desktop/GoLang -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches

-I/usr/local/include -I ./ -g -O2 -o ./_x002.o -c opencvTest.cgo2.c TERM='dumb' gcc -I /home/stefan/Desktop/GoLang -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches

-I/usr/local/include -I ./ -g -O2 -o ./_cgo_main.o -c _cgo_main.c cd /home/stefan/Desktop/GoLang TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches -o $WORK/b001/cgo.o $WORK/b001/_cgo_main.o $WORK/b001/_x001.o $WORK/b001/_x002.o -L/usr/local/lib -lopencv_core -lopencv_video -lopencv_videoio -lopencv_highgui -L/usr/local/lib -lopencv_core -lopencv_video -lopencv_videoio -lopencv_highgui

command-line-arguments /tmp/go-build568047770/b001/_x002.o: In function _cgo_dcf5d601f507_Cfunc_OpenVideo':
  /tmp/go-build/cgo-gcc-prolog:48: undefined reference toOpenVideo' collect2: error: ld returned 1 exit status

[AlexRouSg]

You forgot to include your header in the .cpp file

[StefanCepa]

You are right, My bad. But I still get the same error message

[AlexRouSg]

Are all the files in the same folder?

EDIT:
Just saw your command go build -x opencvTest.go
That will only compile that specific file. You need to do a go build with no args

[StefanCepa]

Oh my .. this actually works now. Thank you! Could you tell me how come?

[AlexRouSg]

I just explained it in the earlier post, giving it a file(s) in the arg literally means compile just the file(s) you gave it no more. So the .cpp file doesn't get compiled and added to the binary cause it wasn't in the list of files to compile. Having no args mean compile the folder in the current working directory.

This is documented at https://golang.org/cmd/go/#hdr-Compile_packages_and_dependencies

For further help I suggest you ask around in one of the places in https://github.com/golang/go/wiki/Questions

[ALTree]

This seems resolved, so I'm closing this issue.