Can't build with Qt 6.8.1

[perdrix52]

Get this error:

CMake Error at CMakeLists.txt:3 (qt_add_library):
  Unknown CMake command "qt_add_library".

command used was:

cmake -B ../build -G Ninja -DQT_VERSION_MAJOR=6 -DCMAKE_INSTALL_PREFIX:STRING="/usr/local" -DCMAKE_MODULE_PATH:STRING="/usr/share/cmake-3.28/Modules" -D CMAKE_PREFIX_PATH:STRING="/opt/Qt/6.8.1/gcc_64"

PS I'd still greatly appreciate being able to build this as a static library. If I can find the time would you accept a pull request to allow that?

Cheers, David

[perdrix52]

Arrgh trying to build using a set of instructions assuming the top level CMakeLists.txt file is in src dir, whereas it is NOW in the to level dir (since 3 days ago).

Still would like to know if you will accept a pull request.

[attila-tokes]

Hi @perdrix52! 🙂 What is your use case for which static linking would work better?

The library is licensed under LGPL, so building it as a static library could just cause unnecessary licensing issues, while providing little or no benefits over dynamic linking.

[perdrix52]

We have a lot of dependencies that we link statically, and that's much simpler to handle than shipping .so files in our installation and therefore having to handle issues with libpath etc..

D.

[perdrix52]

The other reason for static linking is this:
error while loading shared libraries: libQt6Network.so.6: cannot open shared object file: No such file or directory

If I disable the calls to stuff in SmptMime.so and link the code it works. But if I enable the calls and rebuild I get the above error.

Do you know how to solve that?

[perdrix52]

BTW I think there's an error in your CMakeLists.txt: It says:
set(CMAKE_INSTALL_RPATH “${ORIGIN}”)
but I think it should say:
set(CMAKE_INSTALL_RPATH "$ORIGIN")
See: https://discourse.cmake.org/t/help-with-shared-libraries-on-linux/13203

[perdrix52]

I found out why the library isn't built with RPATH/RUNPATH set to $ORIGIN.

1. It should be set(CMAKE_INSTALL_RPATH $ORIGIN)
2. You should set this and the other related variables in the TOP level CMake file, not in the lower level files and they should be set before any targets are defined. Also remove them from the lower level CMake files.

See Craig Scott's (*) comments in the CMake discourse thread referenced in my previous comment.

So the top level CMakeList.txt should read:

cmake_minimum_required(VERSION 3.16)

project(SmtpMime
  VERSION 2.0
  LANGUAGES C CXX)

option(BUILD_TESTS "builds tests" ON)
option(BUILD_DEMOS "builds demos" ON)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_AUTOUIC OFF)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC OFF)

find_package(QT NAMES Qt6 COMPONENTS Core Network Test REQUIRED)
find_package(Qt${QT_VERSION_MAJOR} COMPONENTS Core Network Test REQUIRED)

set(LIBRARY_TARGET_NAME ${PROJECT_NAME})

message(USING Qt${QT_VERSION_MAJOR})

set(CMAKE_SKIP_BUILD_RPATH FALSE)
set(CMAKE_BUILD_WITH_INSTALL_RPATH TRUE)
set(CMAKE_INSTALL_RPATH $ORIGIN)

add_subdirectory(src)

if (BUILD_TESTS)
  add_subdirectory(test)
endif()

if (BUILD_DEMOS)
  add_subdirectory(demos)
endif()

With those changes the library is built correctly with $ORIGIN set in RUNPATH

(*) Craig Scott - author of Professional CMake.

[perdrix52]

Do you want me to fork the project and create a PR for this or will you apply the changes yourself?

Thanks, David

[EgorWeders]

The other reason for static linking is this: error while loading shared libraries: libQt6Network.so.6: cannot open shared object file: No such file or directory

If I disable the calls to stuff in SmptMime.so and link the code it works. But if I enable the calls and rebuild I get the above error.

Do you know how to solve that?

You need to find and link the Qt "Network" package to your project in a subdirectory (also put the .so next to the release executable). Because the .so calls to other libraries depend on your linking. Also try clearing the cmake cache.
Another problem might be that you built SmptMime.so with a different qt kit (or cmake config) than your project (Debug Release mix).

P.S. Just trying to help with the same error we encountered once

[perdrix52]

That wasn't the problem - the problem was the cmake files and r(un)path settings.

[bluetiger9]

Fixed. Thx!