Link dylib in macOs QT project - c++

Question

I tried a simple dylib in macOS and compiled with g++. I made a small sample to test the lib, it works perfect.
Now I made a simple QT app, linked the lib and added the header to the mainwindow.cpp and I always got a fail message Reason: image not found
I read the web and also some other cases here but all is basing on paths.I think it is is not a path problem. Because I made all changes I read in all the cases and also copied the lib in all needed folders, like project folder, build folder. Nothing helps.
I think that QT cannot work with the library and I missed some needed code, like for initialize or export. So that the problem is more inside the dylib and not in QT or Paths values.
Maybe someone can help me here out?
I have tried:
INCLUDEPATH += $$PWD/mylib
DEPENDPATH += $$PWD/mylib
macx: LIBS += -L$$PWD/mylib/ -lmylib
I tried to copy the lib to the build folder and also to the executable folder.
Also edited:
/⁨Users⁩/⁨ingoforster⁩/Documents⁩/Development⁩/Playground⁩/TestGround⁩/mylib:/Users/ingoforster/Qt/5.9.1/clang_64/lib
in Project settings DYLD_LIBRARY_PATH
Set also to DYLD_FRAMEWORK_PATH
Cpp
#include "mylib.hpp"
char *mMessage(void) {
return "Ein sonniger Tag";
}
header
#include <stdio.h>
#include <iostream>
using namespace std;
char *mMessage(void);
compiled with
g++ -std=c++0x --verbose -dynamiclib -o libmylib.dylib mylib.cpp
Sample
#include "mylib.hpp"
int main(void){
char* Ingo = mMessage();
std::cout << mMessage();
}
compiled with
g++ -std=c++0x test.cpp -L./ -lmylib
Actual result is that the sample runs perfect.
But in QT I got:
dyld: Library not loaded: libmylib.dylib
Referenced from: /Users/ingoforster/Documents/Development/Playground/build-TestGround-Desktop_Qt_5_9_1_clang_64bit-Debug/TestGround.app/Contents/MacOS/TestGround
Reason: image not found
10:09:05: The program has unexpectedly finished.
10:09:05: The process was ended forcefully.

Answer 1

/Users/ingoforster/Documents/Development/Playground/build-TestGround-Desktop_Qt_5_9_1_clang_64bit-Debug/TestGround.app/Contents/MacOS/TestGround appears to be compile-linked to your library code but perhaps has not been formally installed to the executable. macdeployqt usually deals with this issue.
You may also do this manually with otool and install_name_tool:
otool -L /path/to/executable
This will list the installed paths to the dylibs in use. You will see your dylib, that is the "/old/path/to/libmylib.dylib"
install_name_tool -change /old/path/to/libmylib.dylib /new/path/to/libmylib.dylib /path/to/executable
Usually, in an .app, the dylib is installed to a subdirectory within the .app folder.
Application.app/
Contents/
MacOS/
executable
Frameworks/
libmylib.dylib
With install_name_tool you can point to the dylib relative to the executable path to make the app portable.
install_name_tool -change /old/path/to/libmylib.dylib #executable_path/../Frameworks/libmylib.dylib /path/to/executable

Answer 2

After some hard investigation and running into the wrong direction with the given answers here I found out, that QTCreator will do all its own:
QTCreator Pro file have to contain:
macx: LIBS += -L$$PWD/mylib/ -lmylib
INCLUDEPATH += $$PWD/mylib
DEPENDPATH += $$PWD/mylib
MediaFiles.files += mylib/libmylib.dylib
MediaFiles.path = Contents/MacOS
QMAKE_BUNDLE_DATA += MediaFiles