Important: Please read the Qt Code of Conduct -

Compilation Error 3

  • I am developing a Qt dll project (SampleCOMDll.dll) with a library project named "samplelibrary" in Qt 5.2.1. using Qt Creator 3.0.1.
    On compilation I am getting a errors (Error 3).

    How do I fix this? Do I need any other pack to be installed.

    Project Details:
    I created an empty dll project named "SampleCOMDll" and a then a library project named "samplelibrary" (Template: Library --> C++ Library --> Shared Library)
    And I have an created an object for "samplelibrary" in "SampleCOMDll".

    On compilation of "SampleCOMDll" project, my application is giving a compile Error 3 without generating the idl file.
    But "SampleCOMDll.dll" is getting generated. I am not able to use the .dll in my application. (Error details are listed below).

    How do I fix this? Do I need any other pack to be installed?

    Also I observed that if I do not craete any object of "samplelibrary" in "SampleCOMDll", there are no compilation errors and idl is generated.

    P.S: I am using installation from pack "qt-opensource-windows-x86-mingw48_opengl-5.2.1.exe" and I have Microsoft Visual Studio 2008 installed.

    Compile output has the following errors.

    bq. C:\Qt\Qt5.2.1\5.2.1\mingw48_32\bin\idc.exe debug\SampleCOMDll.dll /idl debug/SampleCOMDll.idl -version 1.0
    Couldn't load library file debug\SampleCOMDll.dll
    Class has no metaobject information (error in debug\SampleCOMDll.dll)!
    Makefile.Debug:78: recipe for target 'debug\SampleCOMDll.dll' failed
    mingw32-make[1]: [debug\SampleCOMDll.dll] Error 3 (ignored)

    I am giving my Project Details below:

    Project "" File:

    @TEMPLATE = lib
    TARGET = SampleCOMDll

    CONFIG += warn_off dll
    QT += axcontainer
    QT += axserver
    QT += widgets
    QT += opengl
    QT += core
    RC_FILE = SampleCOMDll.rc
    DEF_FILE = SampleCOMDll.def
    HEADERS +=
    SOURCES +=

    win32: LIBS += -L$$PWD/../Bin/debug/ -lSampleLibrary
    INCLUDEPATH += $$PWD/../Bin/debug
    DEPENDPATH += $$PWD/../Bin/debug@

    Project "samplelibrary" File:

    @QT += widgets opengl

    TARGET = SampleLibrary
    TEMPLATE = lib


    SOURCES += samplelibrary.cpp

    HEADERS += samplelibrary.h

    unix {
    target.path = /usr/lib
    INSTALLS += target

  • Moderators

    MinGW and MSVC compilers are not compatible, you should use the same compiler for compiling both projects (I am not sure whether you are doing that or not).

  • Thanks for the reply.

    I am actually using Qt Creator 3.0.1 to compile both the projects. I hope QT Creator IDE uses MinGW compilers. Am I correct?

  • Moderators

    Most probably you are. You can check it in your project settings ("Project" panel on the keft hand side of Qt Creator window).

  • Moderators

    I noticed the compile is trying to use a dll. If you are using qt creator and mingw then DLLs would be named as .so files and libs would be .a. So if it is trying to use a DLL inside of a mingw project it won't work, and would indeed say it couldn't find any symbols.

    Looks like what sierdzio said is happening and you are mixing 2 different compilers/binaries.

Log in to reply