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

Warrior · 8 Feb 2021, 18:06

I've been trying to use the https://github.com/OpenImageDenoise/oidn#compiling-on-linuxmacos library in my code on Linux but still have no luck as of now. Apparently it seems that I am not linking the library properly but the normal ways to link the library also do not seem to work.

Here's what I've done so far: after compiling OIDN I moved the oidn directory to the directory where my path tracer code is and did the following in my code (C++11) which I'm working on in Qt Creator.

#include "oidn/include/OpenImageDenoise/oidn.hpp"
.
.
.
oidn::DeviceRef device = oidn::newDevice(); // this is where things break
device.commit();

Note that doing #include "oidn/include/OpenImageDenoise/oidn.hpp" seems to work fine because autocomplete works for oidn and shows its members. However I get the following errors which seems to be due to not linking oidn libraries.

I tried linking the libraries via LIBS += -L"oidn/build/" or LIBS += -L"oidn/build/libOpenImageDenoise.so" (as shown in the image) but I get the same errors. I also tried LIBS += -L oidn/build -lOpenImageDenoise but got the error message "cannot find -lOpenImageDenoise". I am now pretty confused on what I'm supposed to do. I'm not even sure if the errors are due to not properly linking libraries because I see people generally link libraries in C++ the same way I am trying to do it here. I would really appreciate if someone can help me figure out what I need to do to get OIDN work.

SGaist · wrote on 8 Feb 2021, 17:52

Hi and welcome to devnet,

Where did you install that library on your system ?

Warrior · 2 Aug 2021, 18:01

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 · 8 Feb 2021, 18:12

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 · wrote on 8 Feb 2021, 18:06

@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 · 2 Aug 2021, 18:13

@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 · S SGaist 8 Feb 2021, 18:05

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

JonB · 8 Feb 2021, 19:26

@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 · J JonB 8 Feb 2021, 18:52

@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 · 8 Feb 2021, 19:36

Can your show your .pro file content ?

Warrior · 2 Aug 2021, 19:37

@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 · 8 Feb 2021, 19:58

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 · 9 Feb 2021, 05:53

@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 · 9 Feb 2021, 12:37

@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 · 9 Feb 2021, 12:39

@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 · wrote on 9 Feb 2021, 12:39

This post is deleted!

jsulm · 9 Feb 2021, 12:49

@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 · 9 Feb 2021, 12:55

@jsulm Well the folder definitely does contain the libs:

JonB · 9 Feb 2021, 13:15

@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 · 9 Feb 2021, 13:33

@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.