Cannot link Qt static libraries

  • Hi all,

    I want to deploy a stand-alone application for Windows 32 bit with MinGW using Qt Creator.

    I followed this guide to build Qt statically for Windows (MinGW) and the building process went just fine.

    Then, as suggested by the guide, I opened Qt creator and defined a new Kit which uses the new Qt Static version I just built (by linking its qmake.exe). My previously developed project obviously complained (many errors referring to "undefined reference to") when I switched to the other kit that he could not find any reference for the used Qt functions and classes.

    In order to tell Qt how to find the libraries I changed the .pro file as follows (I used the Qt UI for linking libraries):

    # Project created by QtCreator 2016-09-28T14:09:58
    QT       += core gui
    greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
    TARGET = String_GUI
    TEMPLATE = app
    CONFIG += static
    SOURCES += main.cpp\
    HEADERS  += fontdaemon.h
    INCLUDEPATH += $$PWD/../../../../Qt/Static/5.7.0/include
    DEPENDPATH += $$PWD/../../../../Qt/Static/5.7.0/include
    win32: LIBS += -L$$PWD/../../../../Qt/Static/5.7.0/lib/ -lQt5Core //Example of including one library
    win32-g++: PRE_TARGETDEPS += $$PWD/../../../../Qt/Static/5.7.0/lib/libQt5Core.a

    But even including all the libraries present in the library folder (I put just one for simplicity, but I tried to include all of them), I still get the same number (aboyut 300) of errors "undefined reference to", for example:

    C:\Users\Documents\String_GUI\main.cpp:-1: error: undefined reference to `QApplication::QApplication(int&, char**, int)' 

    It seems my project does not find any reference of the Qt tools in the libraries I link it against. Any insight of what could be the problem?

    I have noticed that the static libraries of my Qt static building have the *.a extension instead of the expected (by me) *.lib ; could this be a problem? The compiler anyway does not complain that he cannot find the libraries, so I guess not, but who knows...

    Moreover, how can I know which static libraries I need to link my project against, depending on the Qt header files I include for definition?

    Thanks in advance.

  • @CBenussi

    You might be right with your assumption, but the error message you are showing is referring to a constructor which does not exist.
    QApplication has an integer and pointers to "strings" (char **). I wonder you got the compilation done with this parameter list.

  • The problem is that Qt is not loading at all the static libraries, since none of the objects I use in my application (QLabel, QLineEdit, QFont...) has a reference to. It compiles perfectly by using the Qt version downloaded with the dll's anyway.

  • *.a are libraries compiled with mingw
    *.lib are libraries compiled with Visual Studio
    QApplication is for graphical I think, so I believe you missed some libraries to link.
    try with Qt5Widgets.a and qmain.a.

    (sorry for my bad english)

  • I tried to link all the libraries present in lib/, include Qt5Widgets and qmain

  • Any hint?

    I could have found a problem. When defining the Kit for the Static version of Qt, I get the following warning for the Qt version:
    "no qmlscene installed":

    alt text

    And then under the kit definition qt tells me that: "The compiler MinGW (x86-windows-msys-pe-32bit) may not produce code compatible with the Qt version (x86-windows-unknown-pe-32bit) installed.
    Could this be the cause?

  • I found the "super silly" problem. I had two versions of MinGW, and I've built the static version of Qt with one, but was defining the kit with the other one. Now it works fine.

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