How to link an external library in Qt Creator when LIBS += -L“…” and -l don't seem to work?

[Warrior]

I'm not sure what you mean by "install" but I followed the steps described in the Intel Open Image Denoise page (https://github.com/OpenImageDenoise/oidn#compiling-on-linuxmacos) to compile the package via cmake and make. I first cloned the OIDN repo somewhere outside my code directory (~/Desktop/pathtracer). Then after compilation I moved the oidn directory to ~/Desktop/pathtracer. You can see the directories below to get a better idea about the structure of my files:

pathtracer directory:

pathtracer/oidn directory:

pathtracer/oidn/build directory:

pathtracer/oidn/include directory:

pathtracer/oidn/include/OpenImageDenoise directory (I'm supposed to use the .hpp file since I am using C++11:

[SGaist]

Then you should use the full path to the folder containing your library in the -L statement of your Qt project as the current location is not part of any search paths used by the linker.

[Pablo J. Rogina]

@Warrior said in How to link an external library in Qt Creator when LIBS += -L“…” and -l don't seem to work?:

if someone can help me figure out what I need to do to get OIDN work.

Have you already checked this article "Third Party Libraries"?

In particular this line:

LIBS += -L"3rdparty/CatWhisperer/lib" -lCatWhisperer

In addition, you may want to consider installing/having the library "outside" your project, since what will happen if you need to create another different project (Qt app) using that same library? Are you going to duplicate the headers/.so files into the new project? I don't think so...

[Warrior]

@SGaist I used the followings and still get the errors cannot find -lOpenImageDenoise or cannot find -loidn. Am I supposed to do something else?
LIBS += -L "/home/Warrior/Desktop/pathtracer/oidn/build" -lOpenImageDenoise
LIBS += -L "/home/Warrior/Desktop/pathtracer/oidn/build" -loidn

[Warrior]

@SGaist Also, how can I add the library paths to the search path you mentioned? Maybe that makes my life easier

[JonB]

@Warrior said in How to link an external library in Qt Creator when LIBS += -L“…” and -l don't seem to work?:

LIBS += -L"oidn/build/"

Although you say you started your -L like this and things still didn't work, why have you changed over to LIBS += -L oidn/build from then on always? I cannot test, but I see no evidence from man gcc that you can put a space between -L and the directory name, and no examples do. I'd start by removing it, in case....

[Warrior]

@JonB Thanks for noticing this. I also tried with the following and still get the same error of cannot find -lOpenImageDenoise:
LIBS += -L"/home/Warrior/Desktop/pathtracer/oidn/build" -lOpenImageDenoise

Any other thoughts? :( This is really strange. I'm not sure what else I need to do.

[SGaist]

Can your show your .pro file content ?

[Warrior]

@SGaist Sure. There you go:

QT += gui
QT += xml

CONFIG += c++11 console
CONFIG -= app_bundle

# The following define makes your compiler emit warnings if you use
# any feature of Qt which as been marked deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

QMAKE_CXXFLAGS += -msse2
QMAKE_CXXFLAGS += -fopenmp
LIBS += -fopenmp
LIBS += -L"/home/Warrior/Desktop/pathtracer/oidn/build/" -lOpenImageDenoise



SOURCES += main.cpp \
    pathtracer.cpp \
    scene/scene.cpp \
    BVH/BBox.cpp \
    BVH/BVH.cpp \
    scene/camera.cpp \
    scene/basiccamera.cpp \
    util/CS123XmlSceneParser.cpp \
    scene/shape/mesh.cpp \
    scene/shape/triangle.cpp

HEADERS += \
    pathtracer.h \
    scene/scene.h \
    BVH/BBox.h \
    BVH/BVH.h \
    BVH/IntersectionInfo.h \
    BVH/Log.h \
    BVH/Object.h \
    BVH/Ray.h \
    BVH/Stopwatch.h \
    scene/camera.h \
    scene/basiccamera.h \
    util/CS123Common.h \
    util/CS123ISceneParser.h \
    util/CS123SceneData.h \
    util/CS123XmlSceneParser.h \
    scene/shape/Sphere.h \
    scene/shape/mesh.h \
    scene/shape/triangle.h \
    util/tiny_obj_loader.h \
    BVH/vector3.h \
    oidn/include/OpenImageDenoise/oidn.hpp \
    oidn/include/OpenImageDenoise/config.h \
    oidn/build/mkl-dnn/include/dnnl_config.h \

INCLUDEPATH += "Eigen/"
INCLUDEPATH += "oidn/include/OpenImageDenoise"
INCLUDEPATH += "oidn/build/mkl-dnn/include/"
INCLUDEPATH += "/oidn/build/"

DISTFILES += \
    README.txt

[SGaist]

That is looking good...
Did you do a full rebuild after modifying these paths ?
Also, did you check that all the symlinks of libOpenImageDenoise are valid and pointing to valid files ?

[Warrior]

@SGaist Yes I did do a clean compilation but got the same error. I did not however check the symlinks you mentioned. How can I do that?

[jsulm]

@Warrior said in How to link an external library in Qt Creator when LIBS += -L“…” and -l don't seem to work?:

How can I do that?

ls -lh /home/Warrior/Desktop/pathtracer/oidn/build/

What is the output of this command?

[Warrior]

@jsulm Apparently the files don't show up. Could it be because I cloned and built oidn in another directory first and then moved everything to the path where my program is? or is there a way to fix the symlink issue?

ls -lh /home/Warrior/Desktop/pathtracer/oidn/build/
total 160K
drwxrwxr-x 4 Warrior Warrior 4.0K Feb  4 00:09 apps
-rw-rw-r-- 1 Warrior Warrior  19K Feb  4 00:09 CMakeCache.txt
drwxrwxr-x 7 Warrior Warrior 4.0K Feb  4 00:09 CMakeFiles
-rw-rw-r-- 1 Warrior Warrior 6.5K Feb  4 00:09 cmake_install.cmake
drwxrwxr-x 3 Warrior Warrior 4.0K Feb  4 00:09 common
-rw-r--r-- 1 Warrior Warrior 3.6K Feb  4 00:09 CPackConfig.cmake
-rw-r--r-- 1 Warrior Warrior 4.0K Feb  4 00:09 CPackSourceConfig.cmake
-rw-rw-r-- 1 Warrior Warrior 103K Feb  4 00:09 Makefile
drwxrwxr-x 3 Warrior Warrior 4.0K Feb  4 00:08 mkl-dnn
-rw-r--r-- 1 Warrior Warrior 1.6K Feb  4 00:09 OpenImageDenoiseConfigVersion.cmake

[jsulm]

This post is deleted!

[jsulm]

@Warrior said in How to link an external library in Qt Creator when LIBS += -L“…” and -l don't seem to work?:

or is there a way to fix the symlink issue?

Your current issue is not related to sym-links. Your problem is that the folder you pass via -L does NOT contain the libs. Either put them back to this folder or pass the folder containing the libs via -L.

[Warrior]

@jsulm Well the folder definitely does contain the libs:

[JonB]

@Warrior
Well you can see for yourself that the listing from ls does not match the files/directories in your screenshot.

My guess is that screenshot does not come from navigating to the same directory. (A screenshot from file manager without proof of what directory is showing is not much use.) So you need to look closely to sort this out....

[Warrior]

@JonB I totally understand the suspicious discrepancy between the screen shot and the directory listing but I am not trying to be funny and take people's time. They're both from the same path. I think I need to clone the oidn repo in the same directory where my code is and build it there. That can hopefully solve the problem.

[Christian Ehrlicher]

@Warrior said in How to link an external library in Qt Creator when LIBS += -L“…” and -l don't seem to work?:

They're both from the same path.

No matter what you tell us - no they're not from the same path. Make sure you use the right one and think about e.g. case sensitivity.

[JonB]

@Warrior said in How to link an external library in Qt Creator when LIBS += -L“…” and -l don't seem to work?:

They're both from the same path.

Can you show us what the file manager says the path it is showing is?