I am trying to install and use Qt 5 on Ubuntu. Running CMake for my project which requires Qt 5 leads to:
-- The C compiler identification is GNU 4.8.4
-- The CXX compiler identification is GNU 4.8.4
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Warning at /usr/local/share/cmake-3.2/Modules/FindQt4.cmake:626 (message):
/usr/bin/qmake reported QT_INSTALL_LIBS as "/usr/lib/x86_64-linux-gnu" but
QtCore could not be found there. Qt is NOT installed correctly for the
target build environment.
I attempted hints from
https://askubuntu.com/questions/508503/whats-the-development-package-for-qt5-in-14-04
https://www.kdab.com/using-cmake-with-qt-5/
How to find and use Qt 5 with CMake?
I added the correct "CMAKE_PREFIX_PATH" as advised by usr1234567
(should it not be made by the installer?)
added the include directories following
https://www.kdab.com/using-cmake-with-qt-5/
(should it not be included in the manual http://doc.qt.io/qt-5/cmake-manual.html, and the KDevelop-generated CMakeLists.txt ?), furthermore the source file generating the GUI elements
(after changing the #include directories from QtGui to QtWidgets, should it not be made by KDevelop?)
I transformed the CMakeLists.txt to what shown. Maybe not optimal, but works.
(it is my very first attempt with Qt, and I guess the mentioned difficulties can discourage people who prefer out-of-box solutions)
cmake_minimum_required(VERSION 2.8.11)
project(MyFirst)
# Find includes in corresponding build directories
set(CMAKE_INCLUDE_CURRENT_DIR ON)
# Instruct CMake to run moc automatically when needed.
set(CMAKE_AUTOMOC ON)
# Find the QtWidgets library
find_package(Qt5Widgets)
# Tell CMake to create the helloworld executable
add_executable(MyFirst main.cpp MyFirst.cpp)
# The Qt5Widgets_INCLUDES also includes the include directories for
# dependencies QtCore and QtGui
include_directories(${Qt5Widgets_INCLUDES})
# We need add -DQT_WIDGETS_LIB when using QtWidgets in Qt 5.
add_definitions(${Qt5Widgets_DEFINITIONS})
# Executables fail to build with Qt 5 in the default configuration
# without -fPIE. We add that here.
set(CMAKE_CXX_FLAGS "${Qt5Widgets_EXECUTABLE_COMPILE_FLAGS}")
# Use the Widgets module from Qt 5.
target_link_libraries(MyFirst Qt5::Widgets)
Have a look at the Qt 5 documentation containing a section on how to use CMake: http://doc.qt.io/qt-5/cmake-manual.html
It provides an example:
cmake_minimum_required(VERSION 2.8.11)
project(testproject)
# Find includes in corresponding build directories
set(CMAKE_INCLUDE_CURRENT_DIR ON)
# Instruct CMake to run moc automatically when needed.
set(CMAKE_AUTOMOC ON)
# Find the QtWidgets library
find_package(Qt5Widgets)
# Tell CMake to create the helloworld executable
add_executable(helloworld WIN32 main.cpp)
# Use the Widgets module from Qt 5.
target_link_libraries(helloworld Qt5::Widgets)
Mind the line containing find_package which differs from your line. It also contains advice, how you can help CMake finding your Qt installation:
In order for find_package to be successful, Qt 5 must be found below
the CMAKE_PREFIX_PATH, or the Qt5_DIR must be set in the CMake
cache to the location of the Qt5WidgetsConfig.cmake file. The easiest
way to use CMake is to set the CMAKE_PREFIX_PATH environment variable
to the install prefix of Qt 5.
Further reading: CMake: Finding Qt5 the right way
