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Thread: error LNK2019: unresolved external symbol

  1. 6th February 2013, 13:26 #1
    Baso
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    Default 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
    Qt Code: 
    1. #-------------------------------------------------
    2. #
    3. # Project created by QtCreator 2013-02-02T23:22:32
    4. #
    5. #-------------------------------------------------
    6.  
    7. QT += core gui
    8.  
    9. greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
    10.  
    11. TARGET = first
    12. TEMPLATE = app
    13. SOURCES += main.cpp\
    14.         mycalculator.cpp \
    15.     display.cpp
    16.  
    17. HEADERS  += mycalculator.h \
    18.     display.h
    19.  
    20. OTHER_FILES += \
    21.     Comments.txt
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    The .h file
    Qt Code: 
    1. #ifndef MYCALCULATOR_H
    2. #define MYCALCULATOR_H
    3. #include <QPushButton>
    4. #include <QTextEdit>
    5. #include "display.h"
    6. class MyCalculator : public QWidget
    7. {
    8.     Q_OBJECT
    9. public:
    10.     MyCalculator(QWidget *parent = 0);
    11.     //QSize sizeHint() const;
    12. private:
    13.     Display *mydisplay;
    14.     enum{digitArrayIndex = 10};
    15.     QPushButton *digitButtons[digitArrayIndex];
    16.     QPushButton *addButton,*subButton,*mulButton,*divButton;
    17.     //there is 6 functions for now
    18.     QPushButton *sinButton,*cosButton,*tanButton;
    19.     QPushButton *powerButton,*sqrtButton,*lnButton;
    20.     QPushButton *equalButton,*pointButton,*clearButton,*delButton,*ansButton;
    21. private slots:
    22.     void digitClicked();
    23.     void operationClicked();
    24.     void functionClicked();
    25.     void equalClicked();
    26.     void pointClicked();
    27.     void clearClicked();
    28.     void delClicked();
    29.     void ansClicked();
    30. private:      //functions
    31.     QPushButton *createButton(const QString &text, const char *buttonSlot);
    32. };
    33. #endif // MYCALCULATOR_H
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    The .cpp file
    Qt Code: 
    1. #include <QGridLayout>
    2. #include <QScrollArea>
    3. #include "mycalculator.h"
    4. #include "display.h"
    5. MyCalculator::MyCalculator(QWidget *parent)
    6.     : QWidget(parent)
    7. {
    8.     QGridLayout *myBasicGrid = new QGridLayout(this);
    9.     myBasicGrid->setSizeConstraint(QLayout::SetFixedSize);
    10.     mydisplay = new Display;
    11.     //display->setReadOnly(true);
    12.     /*QFont displayFont = display->font();
    13.     displayFont.setPointSize(displayFont.pointSize() + 4);
    14.     display->setFont(displayFont);*/
    15.     //Implement operation buttons
    16.     addButton = createButton("+",SLOT(operationClicked()));
    17.     subButton = createButton("-",SLOT(operationClicked()));
    18.     mulButton = createButton("\303\227",SLOT(operationClicked()));
    19.     divButton = createButton("\303\267",SLOT(operationClicked()));
    20.     //Implement function buttons
    21.     sinButton = createButton("sin",SLOT(functionClicked()));
    22.     cosButton = createButton("cos",SLOT(functionClicked()));
    23.     tanButton = createButton("tan",SLOT(functionClicked()));
    24.     powerButton = createButton("x\302\262",SLOT(functionClicked()));
    25.     sqrtButton = createButton("\342\210\232",SLOT(functionClicked()));
    26.     lnButton = createButton("ln",SLOT(functionClicked()));
    27.     //The rest of the buttons
    28.     equalButton = createButton("=",SLOT(equalClicked()));
    29.     pointButton = createButton(".",SLOT(pointClicked()));
    30.     ansButton = createButton("Ans",SLOT(ansClicked()));
    31.     delButton = createButton("DEL",SLOT(delClicked()));
    32.     clearButton = createButton("AC",SLOT(clearClicked()));
    33.     //The digit buttons
    34.     digitButtons[0] = createButton("0",SLOT(digitClicked()));
    35.     for(int i = 1; i<digitArrayIndex; i++){
    36.         digitButtons[i] = createButton(QString::number(i),SLOT(digitClicked()));
    37.         int row = ((9 - i) / 3) + 2;
    38.         int column = ((i - 1) % 3);
    39.         myBasicGrid->addWidget(digitButtons[i],row,column); //Adding the digit buttons to the grid
    40.     }
    41.  
    42.     //layout the display and the rest of the buttons
    43.     //myBasicGrid->addWidget(mydisplay,0,0,1,5);
    44.     myBasicGrid->addWidget(digitButtons[0],5,0);
    45.     myBasicGrid->addWidget(sinButton,1,0);
    46.     myBasicGrid->addWidget(cosButton,1,1);
    47.     myBasicGrid->addWidget(tanButton,1,2);
    48.     myBasicGrid->addWidget(powerButton,1,3);
    49.     myBasicGrid->addWidget(sqrtButton,1,4);
    50.     myBasicGrid->addWidget(delButton,2,3);
    51.     myBasicGrid->addWidget(clearButton,2,4);
    52.     myBasicGrid->addWidget(mulButton,3,3);
    53.     myBasicGrid->addWidget(divButton,3,4);
    54.     myBasicGrid->addWidget(addButton,4,3);
    55.     myBasicGrid->addWidget(subButton,4,4);
    56.     myBasicGrid->addWidget(pointButton,5,1);
    57.     myBasicGrid->addWidget(lnButton,5,2);
    58.     myBasicGrid->addWidget(ansButton,5,3);
    59.     myBasicGrid->addWidget(equalButton,5,4);
    60. }
    61.  
    62. //Slots implemetation
    63. void MyCalculator::digitClicked()
    64. {
    65. }
    66. void MyCalculator::operationClicked()
    67. {
    68. }
    69. void MyCalculator::functionClicked()
    70. {
    71. }
    72. void MyCalculator::equalClicked()
    73. {
    74. }
    75. void MyCalculator::pointClicked()
    76. {
    77. }
    78.  
    79. void MyCalculator::clearClicked()
    80. {
    81. }
    82. void MyCalculator::delClicked()
    83. {
    84. }
    85. void MyCalculator::ansClicked()
    86. {
    87. }
    88. //functions implimintation
    89. QPushButton *MyCalculator::createButton(const QString &text, const char *buttonSlot){
    90.     QPushButton *button = new QPushButton(text);
    91.     connect(button, SIGNAL(clicked()), this, buttonSlot);
    92.     return button;
    93. }
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    and the display.h file // another class I created and Inherited form QTextEdit
    Qt Code: 
    1. #ifndef DISPLAY_H
    2. #define DISPLAY_H
    3.  
    4. #include <QTextEdit>
    5.  
    6. class Display : public QTextEdit
    7. {
    8.     Q_OBJECT
    9. public:
    10.     explicit Display(QWidget *parent = 0);
    11. };
    12. #endif // DISPLAY_H
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    the display.cpp file
    Qt Code: 
    1. ]
    2. #include "display.h"
    3.  
    4. Display::Display(QWidget *parent) :
    5.     QTextEdit(parent)
    6. {
    7. }
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    And here is the error
    Qt Code: 
    1. : 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)
    2. debug\first.exe : fatal error LNK1120: 1 unresolved externals
    3. jom: C:\Users\FBM\Desktop\Calculator\first-build-Desktop_Qt_5_0_1_MSVC2010_32bit-debug\Makefile.Debug [debug\first.exe] Error 1120
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    When I comment the code in line 13 of the .cpp file the program works fine.
    Any help plz
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  2. 6th February 2013, 21:02 #2
    ChrisW67
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    Default Re: error LNK2019: unresolved external symbol

    Run a clean rebuild of the program including rerunning qmake.
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  3. The following 2 users say thank you to ChrisW67 for this useful post:

    Baso (8th February 2013), sami1592 (2nd February 2016)
  4. 8th February 2013, 19:52 #3
    Baso
    Baso is offline Novice
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    Default Re: error LNK2019: unresolved external symbol

    I just deleted the build folder, restart the computer,rebuild and It did work.
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