External prebuilt libraries

vlada

Hi,

since I was solving some problems with external libraries, I realized I don't really understand how it works in QtCreator. There is a guide here and I'm following it.

But it doesn't seem to be working as described there for me. According to the guide, I should put my .dll file to 3rdparty/my_lib/bin/mylib.dll. But this doesn't work. Everything works fine if I put the .dll to 3rdparty/my_lib/lib/mylib.dll

It makes sense, because in the example the bin directory isn't mentioned anywhere in the project file:

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

What am I missunderstanding here?

VRonin

@vlada said in External prebuilt libraries:

But it doesn't seem to be working

What's not working? the compilation or the program doesn't run?

vlada

@VRonin Sorry for not being more specific. Compilation works fine but the program immediately crashes after start because it won't find the shared library.

VRonin

This has nothing to do with Qt. Windows has pre-determined locations where it looks for libraries: https://docs.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-search-order#search-order-for-desktop-applications
99% of the time option 1 is the way to go, 0.9999999% option it's option 6

vlada

@VRonin I don't think this is the case. Maybe I didn't describe it correctly. Let's say this is how my project looks like:

c:\qtapp\myapp\main.cpp
c:\qtapp\myapp\3rdparty\mylib\include\mylib.h
c:\qtapp\myapp\3rdparty\mylib\lib\mylib.dll

Now I compile the app and the .exe will be created in
c:\qtapp\build-myapp-Desktop_Qt_5_13_1_MinGW_32_bit-Release\release\myapp.exe

QtCreator probably adds the path of Qt libraries to the Windows search path, so these are found by the application and I assume it also adds the library path c:\qtapp\myapp\3rdparty\mylib\lib.

This works fine. But according to the guide I linked in my first post, the .dll file should be located in c:\qtapp\myapp\3rdparty\mylib\bin. But this doesn't work. So is the guide wrong?

VRonin

That guide is about compiling a program using a 3rd party library, not deploying it. So the guide is not wrong, it's just not covering this aspect. I suspect that windeployqt will probably recognise the /bin structure and deploy the 3rd party library correctly

vlada

@vronin I'm not talking about deploying. I'm talking about developing my application and running it within QtCreator.

VRonin

developing my application

The linker doesn't need the dll file so its location is irrelevant

running it within QtCreator

That's just an option inside Qt creator: https://doc.qt.io/qtcreator/creator-run-settings.html#selecting-the-run-environment

Just add the path to the bin directory to the PATH variable for the run environment