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Thread: Get a segfault when I setText() a label

  1. 7th October 2010, 21:39 #1
    AGStumps8807
    AGStumps8807 is offline Beginner
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    Default Get a segfault when I setText() a label

    So whenever I call the UpdateLabel function, I get a segmentation fault on the setText() line:

    My Header File:
    Qt Code: 
    1. // MainWin.h
    2. #ifndef _MAINWIN_H
    3. #define _MAINWIN_H
    4. #include <QtGui>
    5. class StampCanv;
    6. class MainWin : public QMainWindow
    7. {
    8.   Q_OBJECT
    9. public:
    10.   MainWin(int argc, char * argv[]);
    11.   ~MainWin();
    12.   void UpdateLabel(int x, int y);
    13.   QLabel *label;
    14. //private slots:
    15. //  void startGame();
    16. //  void exitGame();
    17. //  void updatePlayField();
    18.  
    19. private:
    20.   StampCanv *canv;
    21.   QWidget *centralWidget;
    22.   QListWidget *listWidget;
    23.   QWidget *verticalLayoutWidget;
    24.   QVBoxLayout *verticalLayout;
    25.   QRadioButton *CircleRadio;
    26.   QRadioButton *SquareRadio;
    27.   QRadioButton *TriangleRadio;
    28.   QWidget *verticalLayoutWidget_2;
    29.   QVBoxLayout *verticalLayout_2;
    30.   QRadioButton *RedRadio;
    31.   QRadioButton *GreenRadio;
    32.   QRadioButton *BlueRadio;
    33.  
    34.   QMenuBar *menuBar;
    35.   QMenu *menuFile;
    36.   QMenu *menuShape;
    37.   QMenu *menuHelp;
    38.   //QToolBar *mainToolBar;
    39.   QAction *actionNew;
    40.   QAction *actionOpen;
    41.   QAction *actionSave;
    42.   QAction *actionExit;
    43.   QAction *actionCircle;
    44.   QAction *actionSquare;
    45.   QAction *actionTriangle;
    46.   QAction *actionAbout;
    47.   //QStatusBar *statusBar;
    48. };
    49. #endif
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    And The cpp file, The function is on the bottom:

    Qt Code: 
    1. //MainWin.cpp
    2. #include "MainWin.h"
    3. #include "StampCanv.h"
    4. #include <QtGui>
    5. #include <iostream>
    6. using namespace std;
    7. MainWin::MainWin(int argc, char * argv[])
    8. {
    9.   setObjectName(QString::fromUtf8("MainWin"));
    10.   resize(612, 547);
    11.   setMouseTracking(true);
    12.  
    13.  
    14.         centralWidget = new QWidget;
    15.         centralWidget->setObjectName(QString::fromUtf8("centralWidget"));
    16.         centralWidget->setMouseTracking(true);
    17.         QVBoxLayout * mainLayout = new QVBoxLayout;
    18.         canv = new StampCanv;
    19.         canv->setMouseTracking(true);
    20.         canv->setObjectName(QString::fromUtf8("listWidget"));
    21.         canv->setGeometry(QRect(10, 10, 400, 400));
    22.         canv->setMinimumSize(QSize(400, 400));
    23.         canv->setMaximumSize(QSize(400, 400));
    24.         mainLayout -> addWidget(canv);
    25.         centralWidget -> setLayout(mainLayout); 
    26.  
    27.         verticalLayoutWidget = new QWidget(centralWidget);
    28.         verticalLayoutWidget->setObjectName(QString::fromUtf8("verticalLayoutWidget"));
    29.         verticalLayoutWidget->setGeometry(QRect(430, 140, 160, 71));
    30.         verticalLayout = new QVBoxLayout(verticalLayoutWidget);
    31.         verticalLayout->setSpacing(6);
    32.         verticalLayout->setContentsMargins(11, 11, 11, 11);
    33.         verticalLayout->setObjectName(QString::fromUtf8("verticalLayout"));
    34.         verticalLayout->setContentsMargins(0, 0, 0, 0);
    35.  
    36.         CircleRadio = new QRadioButton(verticalLayoutWidget);
    37.         CircleRadio->setObjectName(QString::fromUtf8("CircleRadio"));
    38.         CircleRadio->setChecked(true);
    39.  
    40.         verticalLayout->addWidget(CircleRadio);
    41.  
    42.         SquareRadio = new QRadioButton(verticalLayoutWidget);
    43.         SquareRadio->setObjectName(QString::fromUtf8("SquareRadio"));
    44.  
    45.         verticalLayout->addWidget(SquareRadio);
    46.  
    47.         TriangleRadio = new QRadioButton(verticalLayoutWidget);
    48.         TriangleRadio->setObjectName(QString::fromUtf8("TriangleRadio"));
    49.  
    50.         verticalLayout->addWidget(TriangleRadio);
    51.  
    52.         verticalLayoutWidget_2 = new QWidget(centralWidget);
    53.         verticalLayoutWidget_2->setObjectName(QString::fromUtf8("verticalLayoutWidget_2"));
    54.         verticalLayoutWidget_2->setGeometry(QRect(430, 230, 160, 65));
    55.         verticalLayout_2 = new QVBoxLayout(verticalLayoutWidget_2);
    56.         verticalLayout_2->setSpacing(6);
    57.         verticalLayout_2->setContentsMargins(11, 11, 11, 11);
    58.         verticalLayout_2->setObjectName(QString::fromUtf8("verticalLayout_2"));
    59.         verticalLayout_2->setContentsMargins(0, 0, 0, 0);
    60.         RedRadio = new QRadioButton(verticalLayoutWidget_2);
    61.         RedRadio->setObjectName(QString::fromUtf8("RedRadio"));
    62.         RedRadio->setChecked(true);
    63.  
    64.         verticalLayout_2->addWidget(RedRadio);
    65.  
    66.         GreenRadio = new QRadioButton(verticalLayoutWidget_2);
    67.         GreenRadio->setObjectName(QString::fromUtf8("GreenRadio"));
    68.  
    69.         verticalLayout_2->addWidget(GreenRadio);
    70.  
    71.         BlueRadio = new QRadioButton(verticalLayoutWidget_2);
    72.         BlueRadio->setObjectName(QString::fromUtf8("BlueRadio"));
    73.  
    74.         verticalLayout_2->addWidget(BlueRadio);
    75.  
    76.         label = new QLabel(this);
    77.         label->setObjectName(QString::fromUtf8("label"));
    78.         label->setGeometry(QRect(430, 120, 60, 13));
    79.         label->setMouseTracking(false);
    80.         setCentralWidget(centralWidget);        
    81.         menuBar = new QMenuBar;
    82.         menuBar->setObjectName(QString::fromUtf8("menuBar"));
    83.         menuBar->setGeometry(QRect(0, 0, 612, 21));
    84.         menuBar->setMouseTracking(false);
    85.         menuFile = new QMenu;
    86.         menuFile->setObjectName(QString::fromUtf8("menuFile"));
    87.         menuFile->setMouseTracking(false);
    88.         menuShape = new QMenu;
    89.         menuShape->setObjectName(QString::fromUtf8("menuShape"));
    90.         menuHelp = new QMenu;
    91.         menuHelp->setObjectName(QString::fromUtf8("menuHelp"));
    92.         menuBar->addMenu(menuFile);
    93.         menuBar->addMenu(menuShape);
    94.         menuBar->addMenu(menuHelp);
    95.  
    96.  
    97.         /*mainToolBar = new QToolBar;
    98.         mainToolBar->setObjectName(QString::fromUtf8("mainToolBar"));
    99.         mainToolBar->setMouseTracking(false);
    100.         addToolBar(Qt::TopToolBarArea, mainToolBar);*/        
    101.  
    102.         actionNew = new QAction(menuFile);
    103.         actionNew->setText("New");
    104.         actionOpen = new QAction(menuFile);
    105.         actionOpen->setText("Open");
    106.         actionSave = new QAction(menuFile);
    107.         actionSave->setText("Save");
    108.         actionExit = new QAction(menuFile);
    109.         actionExit->setText("Exit");
    110.         actionCircle = new QAction(menuShape);
    111.         actionCircle->setText("Circle");
    112.         actionCircle->setCheckable(true);
    113.         actionCircle->setChecked(true);
    114.         actionCircle->setIconVisibleInMenu(true);
    115.         actionSquare = new QAction(menuShape);
    116.         actionSquare->setText("Square");
    117.         actionSquare->setCheckable(true);
    118.         actionTriangle = new QAction(menuShape);
    119.         actionTriangle->setText("Triangle");
    120.         actionTriangle->setCheckable(true);
    121.         actionAbout = new QAction(menuHelp);
    122.         actionAbout->setText("About");  
    123.  
    124.  
    125.         menuBar->addAction(menuFile->menuAction());
    126.         menuBar->addAction(menuShape->menuAction());
    127.         menuBar->addAction(menuHelp->menuAction());
    128.         menuFile->addAction(actionNew);
    129.         menuFile->addAction(actionOpen);
    130.         menuFile->addAction(actionSave);
    131.         menuFile->addAction(actionExit);
    132.         menuShape->addAction(actionCircle);
    133.         menuShape->addAction(actionSquare);
    134.         menuShape->addAction(actionTriangle);
    135.         menuHelp->addAction(actionAbout);
    136.  
    137.         setWindowTitle(QApplication::translate("MainWin", "IPA2", 0, QApplication::UnicodeUTF8));
    138.         CircleRadio->setText(QApplication::translate("MainWin", "Circle", 0, QApplication::UnicodeUTF8));
    139.         SquareRadio->setText(QApplication::translate("MainWin", "Square", 0, QApplication::UnicodeUTF8));
    140.         TriangleRadio->setText(QApplication::translate("MainWin", "Triangle", 0, QApplication::UnicodeUTF8));
    141.         RedRadio->setText(QApplication::translate("MainWin", "Red", 0, QApplication::UnicodeUTF8));
    142.         GreenRadio->setText(QApplication::translate("MainWin", "Green", 0, QApplication::UnicodeUTF8));
    143.         BlueRadio->setText(QApplication::translate("MainWin", "Blue", 0, QApplication::UnicodeUTF8));
    144.         label->setText("(x1, y1)");
    145.         menuFile->setTitle(QApplication::translate("MainWin", "File", 0, QApplication::UnicodeUTF8));
    146.         menuShape->setTitle(QApplication::translate("MainWin", "Shape", 0, QApplication::UnicodeUTF8));
    147.         menuHelp->setTitle(QApplication::translate("MainWin", "Help", 0, QApplication::UnicodeUTF8));
    148.         setMenuBar(menuBar);
    149.  
    150. }
    151. MainWin::~MainWin()
    152. {
    153. }
    154. void MainWin::UpdateLabel(int x, int y)
    155. {
    156.   cout << "UPDATE" << endl;
    157.   cout << "X: " << x << endl;
    158.   cout << "Y: " << y << endl;
    159.   label->setText("(x2,y2)");
    160. }
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    Obviously, I'll change what the update function will change it to later, but I can't even get it to finish the function call.
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  2. 7th October 2010, 22:16 #2
    Lykurg
    Lykurg is offline Guru
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    Default Re: Get a segfault when I setText() a label

    check if label is a valid pointer!
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