Question

我在一本书中使用了一个例子，“C ++ Programming a gui with qt4 second edition”。虽然我目前正在运行qt5，但大多数示例只需要对本书进行细微更改。

但是这个特殊的例子说我需要重载' - ＆gt;'运算符，因为我的一个操作数是类类型的。虽然我已经在Visual c ++中对类使用了这种语法，但它从不抱怨它没有被重载。

错误发生在main.cpp的第11行

以下是代码：

findDialog.h

#ifndef FINDIALOG
#define FINDIALOG

#include <QDialog>

class QCheckBox;
class QLabel;
class QLineEdit;
class QPushButton;

class findDialog : public QDialog  
{
    Q_OBJECT

public:
    findDialog(QWidget *parent = 0);


signals:
    void findNext(const QString &str, Qt::CaseSensitivity cs);
    void findPrevious(const QString &str, Qt::CaseSensitivity cs);
private slots:
    void findClicked();
    void enableFindButton(const QString &text);

private:
    QLabel *label;
    QLineEdit *lineEdit;
    QCheckBox *caseCheckBox;
    QCheckBox *backwardCheckBox;
    QPushButton *findButton;
    QPushButton *closeButton;

};


#endif // FINDIALOG

这是findDialog.cpp

#include <QtWidgets>
#include "findialog.h"

findDialog::findDialog(QWidget *parent) : QDialog(parent)
{
    label = new QLabel(tr("Find &what"));
    lineEdit = new QLineEdit;
    label->setBuddy(lineEdit);

    caseCheckBox = new QCheckBox(tr("Match &case"));
    backwardCheckBox = new QCheckBox (tr("search &backward"));

    findButton = new QPushButton(tr("&Find"));
    findButton->setDefault(true);
    findButton->setEnabled(false);
    closeButton = new QPushButton("&Close");

    connect(lineEdit, SIGNAL(textChanged(const QString &)), this
    SLOT(enableFindButton(const QString &)));                                 
    connect(findButton, SIGNAL(clicked()), this, SLOT(findClicked()));
    connect(closeButton, SIGNAL(clicked()), this, SLOT(close()));

    QHBoxLayout *topLeftBox = new QHBoxLayout;
    topLeftBox->addWidget(label);
    topLeftBox->addWidget(lineEdit);

    QVBoxLayout *leftBox = new QVBoxLayout;
    leftBox->addLayout(topLeftBox);
    leftBox->addWidget(caseCheckBox);
    leftBox->addWidget(backwardCheckBox);

    QVBoxLayout *rightBox = new QVBoxLayout;
    rightBox->addWidget(findButton);
    rightBox->addWidget(closeButton);
    rightBox->addStretch();

    QHBoxLayout *mainLayout = new QHBoxLayout;
    mainLayout->addLayout(leftBox);
    mainLayout->addLayout(rightBox);
    setLayout(mainLayout);

    setWindowTitle(tr("Find"));
    setFixedHeight(sizeHint().height());
}

void findDialog::findClicked()
{
    QString text = lineEdit->text();

    Qt::CaseSensitivity cs = caseCheckBox->isChecked() ?     
    Qt::CaseSensitive : Qt::CaseInsensitive;

    if(backwardCheckBox -> isChecked())
    {
        emit findPrevious(text, cs);
    }

    else
    {
        emit findNext(text, cs);
    }
}

void findDialog::enableFindButton(const QString &text)
{
    findButton->setEnabled(!text.isEmpty());
}

最后是main.cpp（错误发生在第11行）

#include "mainwindow.h"
#include <QApplication>
#include "findialog.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    findDialog dialog = new findDialog;

    //Error occurs on following line
    dialog->show();
    return a.exec();
}

我也尝试过原始/丑陋的语法：

(*dialog).show();

然而，这给我一个非法的间接错误。

Answer 1

dialog不是指针，因此您无法使用->运算符。

findDialog dialog = new findDialog;

应该是

findDialog *  dialog = new findDialog;
           ^^^ pointer

Answer 2

此行不正确

findDialog dialog = new findDialog;

您正在使用会返回指针的new，它应该是

findDialog* dialog = new findDialog;

没有重载运算符 - ＆gt;

2 个答案: