Qt binary linked to both Qt 5 and (wrongly) to Qt

Question

I have a Qt / ROS / Qwt application. Everything was going fine until I tried to link to Qwt. Note that I'm using Qwt 6.1.2 which should run on Qt 5.5. Indeed, the examples run fine.

When I run my binary, it crashes even if I'm not using Qwt. I just need to link the my code to Qwt for that to happen. And -here is the issue I think-, gdb gives the following error:

ram received signal SIGSEGV, Segmentation fault.
0x00007ffff25eadfc in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4

Which is wrong since the binary should be using Qt 5.5. To make things more weird, ldd gives:

>> ldd dls_gui | grep 'Qt'
    libQt5Widgets.so.5 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libQt5Widgets.so.5 (0x00007f684cadc000)
    libQt5Gui.so.5 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libQt5Gui.so.5 (0x00007f684afad000)
    libQt5Core.so.5 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libQt5Core.so.5 (0x00007f684a867000)
    libQtSvg.so.4 => /usr/lib/x86_64-linux-gnu/libQtSvg.so.4 (0x00007f684862c000)
    libQtGui.so.4 => /usr/lib/x86_64-linux-gnu/libQtGui.so.4 (0x00007f6847979000)
    libQtCore.so.4 => /usr/lib/x86_64-linux-gnu/libQtCore.so.4 (0x00007f6847493000)
    libicui18n.so.54 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libicui18n.so.54 (0x00007f6844e33000)
    libicuuc.so.54 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libicuuc.so.54 (0x00007f6844a85000)
    libicudata.so.54 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libicudata.so.54 (0x00007f684305b000)

How can I be linked to both Qt5 and Qt4? Qwt seems to be linked to only Qt 5.5:

>> ldd /usr/local/qwt-6.1.2/lib/libqwt.so | grep 'Qt'
    libQt5PrintSupport.so.5 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libQt5PrintSupport.so.5 (0x00007fbcee13a000)
    libQt5Svg.so.5 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libQt5Svg.so.5 (0x00007fbcedee5000)
    libQt5OpenGL.so.5 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libQt5OpenGL.so.5 (0x00007fbcedc8e000)
    libQt5Widgets.so.5 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libQt5Widgets.so.5 (0x00007fbced410000)
    libQt5Gui.so.5 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libQt5Gui.so.5 (0x00007fbcecbfc000)
    libQt5Core.so.5 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libQt5Core.so.5 (0x00007fbcec4b7000)
    libicui18n.so.54 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libicui18n.so.54 (0x00007fbcea032000)
    libicuuc.so.54 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libicuuc.so.54 (0x00007fbce9c84000)
    libicudata.so.54 => /home/jcolmenares/Qt/5.5/gcc_64/lib/libicudata.so.54 (0x00007fbce825a000)

My CMakeList.txt file is:

cmake_minimum_required(VERSION 2.8.11)
project(dls_gui)

# Find the QtWidgets library
find_package(Qt5Widgets)
# Find includes in corresponding build directories
set(CMAKE_INCLUDE_CURRENT_DIR ON)

# Qwt related
# list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/cmake_packages")
# find_package(Qwt REQUIRED)
find_path(QWT_INCLUDE_DIR qwt.h HINTS /usr/local/qwt-6.1.2/include)
find_library(QWT_LIBRARY qwt /usr/local/qwt-6.1.2/lib/)
include_directories(${QWT_INCLUDE_DIR})


# catkin related
catkin_package()
find_package(catkin REQUIRED COMPONENTS roscpp sensor_msgs urdf)
include_directories( ${catkin_INCLUDE_DIRS} include)

# source, header and resources files list
set(CPP_SOURCES src/main.cpp src/mainwindow.cpp src/basewidget.cpp src/rosQtNode.cpp 
    src/joints_sliders.cpp src/superslider.cpp src/support_polygon.cpp)

set(CPP_HDRS include/mainwindow.h include/basewidget.h include/rosQtNode.hpp 
    include/joints_sliders.hpp include/superslider.hpp include/support_polygon.hpp)

set(QRC_RESOURCES ${CMAKE_CURRENT_SOURCE_DIR}/dls_gui.qrc)

# Add the include directories for the Qt 5 Widgets module to# the compile lines.
include_directories(${Qt5Widgets_INCLUDE_DIRS} )

# Use the compile definitions defined in the Qt 5 Widgets module
add_definitions(${Qt5Widgets_DEFINITIONS})

# Generate headers from ui files
qt5_wrap_ui(UIS_HDRS src/mainwindow.ui)

# Generate moc files from cpp
qt5_wrap_cpp(MOC_SOURCES ${CPP_SOURCES} ${CPP_HDRS})

# Generate resources 
qt5_add_resources(RESOURCES_RCC ${RESOURCE})

# Add compiler flags for building executables (-fPIE)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${Qt5Widgets_EXECUTABLE_COMPILE_FLAGS} -std=c++11")

## Ros include dirs
include_directories(include ${catkin_INCLUDE_DIRS})

# Tell CMake to create the helloworld executable
add_executable(dls_gui ${CPP_SOURCES}  ${UIS_HDRS} ${MOC_SOURCES} ${QRC_RESOURCES})
add_executable(testRos src/testRos.cpp)
qt5_use_modules(dls_gui Widgets)

#Link the helloworld executable to the Qt 5 widgets library.
target_link_libraries(dls_gui ${QWT_LIBRARY} Qt5::Widgets ${catkin_LIBRARIES} )

target_link_libraries(testRos ${catkin_LIBRARIES})

I don't think this is ROS related, nevertheless, is important to say that the source code is compiled via catkin_make etc.

Last but not least, qmake refers to version 5.5:

>> qmake --version
QMake version 3.0
Using Qt version 5.5.0 in /home/jcolmenares/Qt/5.5/gcc_64/lib

EDIT: Just to be clear: I want (need) everything compiled and linked to the same Qt versión. But somehow, is not happening.

Answer 1

You need to link with qwt-qt5.

qwt is the Qt4 version of QWT, which uses libQtGui.so.4 etc., which you can see in your ldd output above. Linking with qwt-qt5 only requires Qt5 so files.

Answer 2

I switched everything back to Qt4. Got tired of wasting time on an issue that should not happen. Still have no idea how the binary ended linked to two different versions of Qt, only when linked to Qwt, where Qwt was linked only to Qt5 and the binary without the linkage to Qwt was also only linked to Qt5.