File .obj not found on Windows

  • Hi, I wanted to add some new functions to my program I created with free Qt version using my registered one. I use another Windows computer now and it looks like installation of Qt was OK because I can run demo examples. But for some reason although I can see missing files on debug folder I get errors (23 !)
    like this "unresolved external symbol_xxx File not found xxx.obj" I know that I didn't have those errors when I finished the project for 2 years ago! Where can be the problem? I'm not using Qt on Windows on normal case , mostly on Linux, now I have no idea what to do. The function have to be added and delivered to customer 15 August. Any help will be appreciated.

  • Moderators

    @Norrbotten Can you provide the whole build log?

  • Qt Champions 2016

    Also, please delete any .user file in the project folder and re setup the project with the kits.

  • hi, I already did it and nothing happens. I found that the only part of the code with class (C++ class) added to project gives the problem. Project was done on the older version of QT, maybe now is it different way to add classes to the project?
    I created a new a new empty project and just added a C++ class (base class QObject with included Q Widget).
    And it will not work
    #ifndef SOMECLASS_H
    #define SOMECLASS_H

    #include <QObject>
    #include <QWidget>

    class someClass : public QObject
    explicit someClass(QObject *parent = nullptr);


    public slots:
    void DoSomething();

    #endif // SOMECLASS_H


    #include "someclass.h"
    #include <QMessageBox>

    someClass::someClass(QObject *parent) : QObject(parent)


    void someClass::DoSomething()
    QMessageBox msg;


    #include "mainwindow.h"
    #include "ui_mainwindow.h"
    #include "someclass.h"
    someClass *myClass;
    MainWindow::MainWindow(QWidget *parent) :
    ui(new Ui::MainWindow)
    myClass=new someClass(this);

    delete ui;
    mainwindow.obj:-1: error: LNK2019: unresolved external symbol "public: __cdecl someClass::someClass(class QObject *)" (??0someClass@@QEAA@PEAVQObject@@@Z) referenced in function "public: __cdecl MainWindow::MainWindow(class QWidget *)" (??0MainWindow@@QEAA@PEAVQWidget@@@Z)

    debug\TestObjErrors.exe:-1: error: LNK1120: 1 unresolved externals

  • Hi @Norrbotten

    You use explicit with your someClass contructor which means you have to explicitly cast QWidget * (the thisin myClass=new someClass(this);) to QObject * in MainWindow::MainWindow.


  • @m.sue I used this way for few years ago . The software working fin (executable I created at that time) no such problems as I have now I had at that time
    #ifndef GLWIDGET_H
    #define GLWIDGET_H

    #include <QGLWidget>

    class GLWidget : public QGLWidget
    *explicit GLWidget(QWidget parent = 0);

    public slots:
    void RePaint();
    void initializeGL() ;
    void paintGL() ;
    void resizeGL(int w, int h);

    void mouseMoveEvent(QMouseEvent *event);
    void mousePressEvent(QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);


    #endif // GLWIDGET_H
    Must probably the syntactic was changed while I didn't use Qt . How otherwise have I declare the class?

  • Moderators

    @Norrbotten Can you please post the whole build log?

  • Moderators

    @m.sue explicit only tells the compiler to not to use the constructor for implicit type conversions like:

    QObject* obj;
    someClass sClass = obj; // Without explicit compiler would use someClass(QObject *parent = nullptr) constructor to convert QObject* to someClass, with explicit this line will cause a compiler error

  • Hi, in case some one have the same problem.
    I receive help from support.
    in .h have to be

    #include <QtGui/QOpenGLFunctions_1_1>
    class bscanclass : public QGLWidget, QOpenGLFunctions_1_1
    explicit bscanclass(QWidget *parent = 0);

    call from main:
    bscanclass *BscanW; // declaration

    and then
    BscanW=new bscanclass(this);

    Working perfect now. Thank you very much for trying to help

Log in to reply

Looks like your connection to Qt Forum was lost, please wait while we try to reconnect.