Error LNK2019: unresolved external symbol

  • I've been through 20 subject about this error, but I didn't figure how to fix it
    -I'm using Qt 5.0.1, Qtcreatro 2.6.2 - with visual studio 2010 on windows 7 64bit
    Here is my code
    the .pro file

    Project created by QtCreator 2013-02-02T23:22:32


    QT += core gui

    greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

    TARGET = first
    TEMPLATE = app
    SOURCES += main.cpp

    HEADERS += mycalculator.h


    *The .h file *

    @#ifndef MYCALCULATOR_H
    #define MYCALCULATOR_H
    #include <QPushButton>
    #include <QTextEdit>
    #include "display.h"
    class MyCalculator : public QWidget
    MyCalculator(QWidget *parent = 0);
    //QSize sizeHint() const;
    Display *mydisplay;
    enum{digitArrayIndex = 10};
    QPushButton *digitButtons[digitArrayIndex];
    QPushButton *addButton,*subButton,*mulButton,*divButton;
    //there is 6 functions for now
    QPushButton *sinButton,*cosButton,*tanButton;
    QPushButton *powerButton,*sqrtButton,*lnButton;
    QPushButton *equalButton,*pointButton,*clearButton,*delButton,*ansButton;
    private slots:
    void digitClicked();
    void operationClicked();
    void functionClicked();
    void equalClicked();
    void pointClicked();
    void clearClicked();
    void delClicked();
    void ansClicked();
    private: //functions
    QPushButton *createButton(const QString &text, const char *buttonSlot);
    #endif // MYCALCULATOR_H@

    *The .cpp file *

    @#include <QGridLayout>
    #include <QScrollArea>
    #include "mycalculator.h"
    #include "display.h"
    MyCalculator::MyCalculator(QWidget *parent)
    : QWidget(parent)
    QGridLayout *myBasicGrid = new QGridLayout(this);
    mydisplay = new Display;
    //Implement operation buttons
    addButton = createButton("+",SLOT(operationClicked()));
    subButton = createButton("-",SLOT(operationClicked()));
    mulButton = createButton("\303\227",SLOT(operationClicked()));
    divButton = createButton("\303\267",SLOT(operationClicked()));
    //Implement function buttons
    sinButton = createButton("sin",SLOT(functionClicked()));
    cosButton = createButton("cos",SLOT(functionClicked()));
    tanButton = createButton("tan",SLOT(functionClicked()));
    powerButton = createButton("x\302\262",SLOT(functionClicked()));
    sqrtButton = createButton("\342\210\232",SLOT(functionClicked()));
    lnButton = createButton("ln",SLOT(functionClicked()));
    //The rest of the buttons
    equalButton = createButton("=",SLOT(equalClicked()));
    pointButton = createButton(".",SLOT(pointClicked()));
    ansButton = createButton("Ans",SLOT(ansClicked()));
    delButton = createButton("DEL",SLOT(delClicked()));
    clearButton = createButton("AC",SLOT(clearClicked()));
    //The digit buttons
    digitButtons[0] = createButton("0",SLOT(digitClicked()));
    for(int i = 1; i<digitArrayIndex; i++){
    digitButtons[i] = createButton(QString::number(i),SLOT(digitClicked()));
    int row = ((9 - i) / 3) + 2;
    int column = ((i - 1) % 3);
    myBasicGrid->addWidget(digitButtons[i],row,column); //Adding the digit buttons to the grid

    //layout the display and the rest of the buttons


    //Slots implemetation
    void MyCalculator::digitClicked()
    void MyCalculator::operationClicked()
    void MyCalculator::functionClicked()
    void MyCalculator::equalClicked()
    void MyCalculator::pointClicked()

    void MyCalculator::clearClicked()
    void MyCalculator::delClicked()
    void MyCalculator::ansClicked()
    //functions implimintation
    QPushButton *MyCalculator::createButton(const QString &text, const char *buttonSlot){
    QPushButton *button = new QPushButton(text);
    connect(button, SIGNAL(clicked()), this, buttonSlot);
    return button;

    *and the display.h *file // another class I created and Inherited form QTextEdit
    @#ifndef DISPLAY_H
    #define DISPLAY_H

    #include <QTextEdit>

    class Display : public QTextEdit
    explicit Display(QWidget *parent = 0);
    #endif // DISPLAY_H@

    *the display.cpp file *

    @#include "display.h"

    Display::Display(QWidget *parent) :

    And here is the error

    @ : error LNK2019: unresolved external symbol "public: __thiscall Display::Display(class QWidget *)" (??0Display@@QAE@PAVQWidget@@@Z) referenced in function "public: __thiscall MyCalculator::MyCalculator(class QWidget *)" (??0MyCalculator@@QAE@PAVQWidget@@@Z)
    debug\first.exe : fatal error LNK1120: 1 unresolved externals
    jom: C:\Users\FBM\Desktop\Calculator\first-build-Desktop_Qt_5_0_1_MSVC2010_32bit-debug\Makefile.Debug [debug\first.exe] Error 1120@
    When I comment the code in line 13 of the .cpp file the program works fine.
    Any help plz

  • You should include QFont:

    @#include <QFont>@

    In addition, in the .cpp file I cannot see when you create the "display" object:

    /QFont displayFont = display->font();
    displayFont.setPointSize(displayFont.pointSize() + 4);
    //Implement operation buttons@

  • Forget about the font and all of these stuff they are commented ,any way I edited the post and deleted them.
    The creation of the Display object is in line 10

  • Well... I don't see the #include <QWidget> anywhere in your headers

  • [quote author="b1gsnak3" date="1360246401"]Well... I don't see the #include <QWidget> anywhere in your headers[/quote]

    This won't be required as it's part of the inheritance chain.

  • I have tried to compile your program and it runs well for me. May be you could re-generate the Makefile and then clean project and re-compile again?

    When I had these problems I had some methods declared but not implemented. Can ensure yourself that all the code posted is that you have?

    We will solve this issue!

  • What usually works for me is to through away the entire build directory that Qt creates when debugging or running a program. This will remove all files generated by QMake (also your ui files). Then rebuild the program. Problem might be fixed then.

  • Yes Thanks guys It did work after deleting the build folder, restart and rebuild :).

  • I often get such errors, 99.99% of the time it is solved by clicking "clean all" then "run qmake" then "rebuild all".

  • [quote author="utcenter" date="1360368863"]I often get such errors, 99.99% of the time it is solved by clicking "clean all" then "run qmake" then "rebuild all".[/quote]

    The 0.01% remaining could be missing the name space in the .cpp file. For example:

    You define a function in your class header (MyClass.h) :

    @ int myFunction(int a, int b);@

    But in the MyClass.cpp you miss the namespace:

    @int myFunction(int a, int b){
    // ...

    instead of

    @int Class::myFunction(int a, int b){
    // ...

    When calling that "myFunction" in your code, the error appears.

  • Worked for me on a project getting this error code :
    [quote author="utcenter" date="1360368863"]I often get such errors, 99.99% of the time it is solved by clicking "clean all" then "run qmake" then "rebuild all".[/quote]

    Sir, you rock

  • Worked for me on a project getting this error code :
    [quote author="utcenter" date="1360368863"]I often get such errors, 99.99% of the time it is solved by clicking "clean all" then "run qmake" then "rebuild all".[/quote]

    Sir, you rock

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