make cannot find OpenCV libraries during make call

Question

I am trying to make a C++ program from a github repo. I have cloned the repo and cd into it. Per instructions, I run make to build. Here is the original Makefile:

# Makefile for heartbeat
appname := Heartbeat

CXX := g++
RM := rm -f
CXXFLAGS := -Wall -g -std=c++11 -I/usr/local/include/opencv4
LDFLAGS := -g
LDLIBS := -lopencv_core -lopencv_dnn -lopencv_highgui -lopencv_imgcodecs -lopencv_imgproc -lopencv_objdetect -lopencv_video -lopencv_videoio

SRCS := $(shell find . -name "*.cpp")
OBJS = $(subst .cpp,.o,$(SRCS))

all: $(appname)

$(appname): $(OBJS)
    $(CXX) $(CXXFLAGS) $(LDFLAGS) -o $(appname) $(OBJS) $(LDLIBS)

depend: .depend

.depend: $(SRCS)
    $(RM) ./.depend
    $(CXX) $(CXXFLAGS) -MM $^>>./.depend;

clean:
    $(RM) $(appname) $(OBJS)

dist-clean: clean
    $(RM) *~ .depend

include .depend

When I run it, I get this error:

g++ -Wall -g -std=c++11 -I/usr/local/include/opencv4 -g -o Heartbeat ./RPPG.o ./Heartbeat.o ./opencv.o -lopencv_core -lopencv_dnn -lopencv_highgui -lopencv_imgcodecs -lopencv_imgproc -lobjdetect -lopencv_video -lopencv_videoio
ld: library not found for -lopencv_core
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [Heartbeat] Error 1

So I adjusted the -I include path to opencv to reflect where I have it installed on my machine. I have it installed here (and use it frequently in python): Users/asi/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include/opencv2

With this, I made a new Makefile:

# Makefile for heartbeat
appname := Heartbeat

CXX := g++
RM := rm -f
CXXFLAGS := -Wall -g -std=c++11 -I/Users/asi/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include
LDFLAGS := -g
LDLIBS := -lopencv_core -lopencv_dnn -lopencv_highgui -lopencv_imgcodecs -lopencv_imgproc -lobjdetect -lopencv_video -lopencv_videoio

SRCS := $(shell find . -name "*.cpp")
OBJS = $(subst .cpp,.o,$(SRCS))

all: $(appname)

$(appname): $(OBJS)
        $(CXX) $(CXXFLAGS) $(LDFLAGS) -o $(appname) $(OBJS) $(LDLIBS)

depend: .depend

.depend: $(SRCS)
        $(RM) ./.depend
        $(CXX) $(CXXFLAGS) -MM $^>>./.depend;

clean:
        $(RM) $(appname) $(OBJS)

dist-clean: clean
        $(RM) *~ .depend

include .depend

but I still get this error:

g++ -Wall -g -std=c++11 -I/Users/asi/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include   -c -o Heartbeat.o Heartbeat.cpp
g++ -Wall -g -std=c++11 -I/Users/asi/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include   -c -o opencv.o opencv.cpp
g++ -Wall -g -std=c++11 -I/Users/asi/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include -g -o Heartbeat ./RPPG.o ./Heartbeat.o ./opencv.o -lopencv_core -lopencv_dnn -lopencv_highgui -lopencv_imgcodecs -lopencv_imgproc -lobjdetect -lopencv_video -lopencv_videoio
ld: library not found for -lopencv_core
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [Heartbeat] Error 1

I'm not sure what to do. I have all of the libraries installed in the path referenced by my -I call. Why can't make find them?

For reference, I am running on a Mac (Catalina OS).

You need to use `-L` to set the location of the library folder similar to how you used `-I` to add the include path — drescherjm, Sep 04 '20 at 18:44
@MarkSetchell yes. I think I installed cv2 via pip or conda. Should I install via brew instead? — connor449, Sep 04 '20 at 18:56
@drescherjm like this? `g++ -Wall -g -std=c++11 -I/Users/asi/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include -L/Users/asi/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include -g -o Heartbeat ./RPPG.o ./Heartbeat.o ./opencv.o -lopencv_core -lopencv_dnn -lopencv_highgui -lopencv_imgcodecs -lopencv_imgproc -lobjdetect -lopencv_video -lopencv_videoio`. I still get the same error with this. — connor449, Sep 04 '20 at 18:57
`-L/Users/asi/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include` Similar however I don't think the .a or .so files for the opencv libraries are in this folder. You need to use the correct path. — drescherjm, Sep 04 '20 at 18:58

Mark Setchell · Answer 1 · 2020-09-04T21:03:50.647

homebrew more or less always symlinks all binaries it installs from:

/usr/local/Cellar/PACKAGENAME/PACKAGEVERSION

to

/usr/local/bin

so you only need /usr/local/bin on your PATH and you get the latest binaries of all homebrew packages. So,let's look at pdfimages which I installed with homebrew:

ls -l /usr/local/bin/pdfimages
lrwxr-xr-x   1 mark  admin        38 Jul 14 15:54 pdfimages -> ../Cellar/poppler/0.90.1/bin/pdfimages

Likewise, it puts all header files in

/usr/local/include

and all libraries in

/usr/local/lib

so you normally only need the following to compile:

g++ -std=c++XX source.cpp -I /usr/local/include -L /usr/local/lib -lXXX -lYYY -lZZZ -o program

Failing that, just look for your libraries with find and then set -L XXX accordingly:

# Look for OpenCV libraries in /usr, /opt and $HOME
find /usr /opt $HOME -type f -iname "*opencv*so" 2> /dev/null

Alternatively, you can use pkgconfig in exactly the same way as described here.

make cannot find OpenCV libraries during make call

1 Answers1