Qt5在关闭时崩溃

时间：2014-06-16 18:18:29

标签： c++ qt segmentation-fault qt5

我的项目有时会在关闭时崩溃，但不可靠。当使用“取消”按钮关闭时，它比使用转义键关闭时更频繁地崩溃，这进一步让我感到困惑。我有一个简单的查找对话框（较大项目的一小部分）作为测试用例的一种形式。

尝试使用GDB进行调试会导致它永远不会崩溃。核心转储是垃圾（坏内存）。

以下是来源。我无法确定究竟出了什么问题;我已经看到（经过微小修改）双重释放，释放NULL，释放一个从未存在过的指针等等。我开始怀疑它是否是部分Qt的错误。

部首：

#ifndef NIDE_FINDDIALOG_HPP
#define NIDE_FINDDIALOG_HPP

#include <QDialog>
#include <QString>
#include <QGridLayout>
#include <QCheckBox>
#include <QLineEdit>
#include <QPushButton>
#include <QWidget>

class FindDialog: public QDialog {
public:
    bool regex, caseSensitive, inSelection, wholeWord, forward, wrap;
    QString expr;

private:
    struct {
        QGridLayout *layout;
        QCheckBox *regex, *caseSense, *select, *whole, *forward, *wrap;
        QLineEdit *exprBox;
        QPushButton *cancel, *find;
    }ui;

    void onCancel();
    void onFind();

    void onRegex();
    void onCase();
    void onSelect();
    void onWhole();
    void onForward();
    void onWrap();

public:
    FindDialog(QWidget *parent);
    ~FindDialog();
};

#endif/*NIDE_FINDDIALOG_HPP*/

来源：

#include <NIDE/FindDialog.hpp>

FindDialog::FindDialog(QWidget *parent): QDialog(parent),
    regex(false), caseSensitive(true), inSelection(false), wholeWord(true),
    forward(true), wrap(true), expr() {

    ui.layout       = new QGridLayout(this);    
    ui.regex        = new QCheckBox("Regex", this);
    ui.caseSense    = new QCheckBox("Match case", this);
    ui.select       = new QCheckBox("In Selection", this);
    ui.whole        = new QCheckBox("Whole Word", this);
    ui.forward      = new QCheckBox("Forward", this);
    ui.wrap         = new QCheckBox("Wrap around", this);
    ui.exprBox      = new QLineEdit(this);
    ui.cancel       = new QPushButton("Cancel", this);
    ui.find         = new QPushButton("Find", this);

    ui.regex->setChecked(regex);
    connect(ui.regex, &QCheckBox::stateChanged, this, &FindDialog::onRegex);

    ui.caseSense->setChecked(caseSensitive);
    connect(ui.caseSense, &QCheckBox::stateChanged, this, &FindDialog::onCase);

    ui.select->setChecked(inSelection);
    connect(ui.select, &QCheckBox::stateChanged, this, &FindDialog::onSelect);

    ui.whole->setChecked(wholeWord);
    connect(ui.whole, &QCheckBox::stateChanged, this, &FindDialog::onWhole);

    ui.forward->setChecked(forward);
    connect(ui.forward, &QCheckBox::stateChanged, this, &FindDialog::onForward);

    ui.wrap->setChecked(wrap);
    connect(ui.wrap, &QCheckBox::stateChanged, this, &FindDialog::onWrap);

    ui.exprBox->setPlaceholderText(tr("Find expr..."));
    connect(ui.exprBox, &QLineEdit::returnPressed, this, &FindDialog::onFind);

    connect(ui.cancel, &QPushButton::clicked, this, &FindDialog::onCancel);

    ui.find->setDefault(true);
    connect(ui.find, &QPushButton::clicked, this, &FindDialog::onFind);


    ui.layout->addWidget(ui.regex, 0, 0);
    ui.layout->addWidget(ui.caseSense, 0, 1);
    ui.layout->addWidget(ui.select, 0, 2);
    ui.layout->addWidget(ui.whole, 1, 0);
    ui.layout->addWidget(ui.forward, 1, 1);
    ui.layout->addWidget(ui.wrap, 1, 2);
    ui.layout->addWidget(ui.exprBox, 2, 0, 1, 3);
    ui.layout->addWidget(ui.cancel, 3, 1);
    ui.layout->addWidget(ui.find, 3, 2);

    setLayout(ui.layout);

    setWindowTitle(tr("Find"));
}
FindDialog::~FindDialog() {
    delete ui.layout;
    delete ui.regex;
    delete ui.caseSense;
    delete ui.select;
    delete ui.whole;
    delete ui.forward;
    delete ui.wrap;
    delete ui.exprBox;
    delete ui.cancel;
    delete ui.find;
}

void FindDialog::onCancel() {
    done(QDialog::Rejected);
}
void FindDialog::onFind() {
    expr = ui.exprBox->text();
    done(QDialog::Accepted);
}

void FindDialog::onRegex() { regex = ui.regex->isChecked(); }
void FindDialog::onCase() { caseSensitive = ui.caseSense->isChecked(); }
void FindDialog::onSelect() { inSelection = ui.select->isChecked(); }
void FindDialog::onWhole() { wholeWord = ui.whole->isChecked(); }
void FindDialog::onForward() { forward = ui.forward->isChecked(); }
void FindDialog::onWrap() { wrap = ui.wrap->isChecked(); }

主：

#include <NIDE/FindDialog.hpp>

#include <QApplication>

int main(int argc, char **argv) {
    QApplication *app = new QApplication(argc, argv);
    FindDialog fd(NULL);

    app->setApplicationName("NIDE");

    fd.exec();
}

1 个答案:

答案 0 :(得分：2)

在避免使用Q_OBJECT宏时，您依赖于Qt的实施细节。连接到没有Q_OBJECT的类中声明的方法是未定义的行为。它在特定版本的Qt中工作的事实是一个愉快的巧合。

唉，你的代码做了很多不必要的事情。

  1. 没有必要在堆上保留Ui元素或QApplication实例。

  2. 所有onXxxx方法都没有理由，因为在通过exec()显示对话框时，您无法读取对话框的状态。在接受（或可能被拒绝）后，您只关心对话框的状态。

  3. 您可以使用QDialog::accept和QDialog::reject个广告位。

  4. 要在多个平台上正确显示对话框，您应该使用QDialogButtonBox而不是离散按钮。

  5. 最后，使用QDialog::exec()重新进入事件循环，让您认为代码是真的不同步。它是很难找到错误的根源。您只需show()对话框，并在单击“查找”按钮时对其发出的accepted信号作出反应。

    6. 以下代码试图成为一个合理正确的解决方案。它适用于Qt 4和Qt 5。

    // Interface
#include <QDialog>
#include <QGridLayout>
#include <QCheckBox>
#include <QLineEdit>
#include <QDialogButtonBox>

#if QT_VERSION<QT_VERSION_CHECK(5,0,0)
#define Q_DECL_OVERRIDE
#endif

class FindDialog: public QDialog {
   struct Ui {
      QGridLayout layout;
      QCheckBox regex, caseSense, select, whole, forward, wrap;
      QLineEdit exprBox;
      QDialogButtonBox buttonBox;
      Ui(QWidget * widget);
   } m_ui;
   void get();
public:
   bool regex, caseSensitive, inSelection, wholeWord, forward, wrap;
   QString expr;

   FindDialog(QWidget *parent = 0);
   ~FindDialog();
   void set();
   void done(int r) Q_DECL_OVERRIDE;
};

// Implementation
FindDialog::Ui::Ui(QWidget * widget) :
   layout(widget),
   regex(tr("Regex")),
   caseSense(tr("Match case")),
   select(tr("In Selection")),
   whole(tr("Whole Word")),
   forward(tr("Forward")),
   wrap(tr("Wrap around")),
   buttonBox(QDialogButtonBox::Cancel)
{
   layout.addWidget(&regex, 0, 0);
   layout.addWidget(&caseSense, 0, 1);
   layout.addWidget(&select, 0, 2);
   layout.addWidget(&whole, 1, 0);
   layout.addWidget(&forward, 1, 1);
   layout.addWidget(&wrap, 1, 2);
   layout.addWidget(&exprBox, 2, 0, 1, 3);
   layout.addWidget(&buttonBox, 3, 0, 1, 3);
   exprBox.setPlaceholderText(tr("Find expr..."));
   buttonBox.addButton(tr("Find"), QDialogButtonBox::AcceptRole);
}

FindDialog::FindDialog(QWidget *parent): QDialog(parent), m_ui(this),
   regex(false), caseSensitive(true), inSelection(false), wholeWord(true),
   forward(true), wrap(true)
{
   set();
   connect(&m_ui.buttonBox, SIGNAL(rejected()), SLOT(reject()));
   connect(&m_ui.buttonBox, SIGNAL(accepted()), SLOT(accept()));
   setWindowTitle("Find");
}

FindDialog::~FindDialog() {}

void FindDialog::done(int result)
{
   get();
   QDialog::done(result);
}

void FindDialog::get()
{
   regex = m_ui.regex.isChecked();
   caseSensitive = m_ui.caseSense.isChecked();
   inSelection = m_ui.select.isChecked();
   wholeWord = m_ui.whole.isChecked();
   forward = m_ui.forward.isChecked();
   wrap = m_ui.wrap.isChecked();
   expr = m_ui.exprBox.text();
}

void FindDialog::set()
{
   m_ui.regex.setChecked(regex);
   m_ui.caseSense.setChecked(caseSensitive);
   m_ui.select.setChecked(inSelection);
   m_ui.whole.setChecked(wholeWord);
   m_ui.forward.setChecked(forward);
   m_ui.wrap.setChecked(wrap);
}

// Main
#include <QApplication>
#include <QMessageBox>

int main(int argc, char **argv) {
   QApplication app(argc, argv);
   app.setApplicationName("NIDE");
   FindDialog fd;
   fd.show();
#if QT_VERSION>=QT_VERSION_CHECK(5,0,0)
   // This can't be done in Qt4 without using moc
   QObject::connect(&fd, &QDialog::accepted, [&fd]{
      QMessageBox::information(NULL, "Find",
         QString("The user wants to find \"%1\"").arg(fd.expr));
   });
#endif
   return app.exec();
}
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