“重新创建”C++中的对象不会重置属性的值。 (Qt)
问题描述:
我认为将代码放下会更容易,但我想要的是“重新创建”一个对象。 所以在简单的例子中,我有一个int类作为属性的类。当我使用 object = new Object();
重新创建类时,int保持相同的值,但不会重置。“重新创建”C++中的对象不会重置属性的值。 (Qt)
下面是一个简单的问题的代码(它看起来过于复杂,但有一个原因):
的main.cpp
#include <iostream>
#include "main.h"
using namespace std;
int main(int argc, const char * argv[]) {
Object *object = new Object();
object->setNumber(4);
cout << endl << object->getNumber()<<endl;
restart(object);
cout << endl << object->getNumber()<<endl;
return 0;
}
void restart(Object *object)
{
object = new Object();
}
main.h
#ifndef test_main_h
#define test_main_h
#include "object.h"
void restart(Object *object);
#endif
object.cpp
using namespace std;
Object::Object()
{
m_number = new int(2);
}
void Object::setNumber(int number)
{
m_number = new int(number);
}
int Object::getNumber()
{
return *m_number;
}
object.h
#ifndef __test__object__
#define __test__object__
#include <stdio.h>
class Object
{
public:
Object();
void setNumber(int number);
int getNumber();
private:
int *m_number;
};
#endif /* defined(__test__object__) */
所以输出会是:
4
4
Program ended with exit code: 0
我们将在最后的输出需要2。
现在,如果你想知道为什么我做这一切,是因为我正在做一个程序使用Qt,和我有同样的问题,而是一个有点复杂:
的main.cpp
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Main main;
main.show();
return a.exec();
}
mainwindow.h
#ifndef LESSON_H
#define LESSON_H
#include <QAudioProbe>
#include <QAudioRecorder>
#include <QDir>
#include <QFileDialog>
#include <QMediaRecorder>
#include <fstream>
#include <string>
#include <QVariant>
#include <QDir>
#include <QtCore>
#include <QtWidgets>
#include <QMediaPlayer>
#include <QKeyEvent>
class MainWindow : public QWidget
{
Q_OBJECT
public:
MainWindow();
private slots:
void togglePause();
void toggleRecord();
void setEnabled();
signals:
void end();
private:
QPushButton *m_record;
QPushButton *m_recordPause;
QPushButton *m_enableB;
bool m_enable;
QLabel *m_recordState;
QMediaPlayer *m_audio;
QAudioRecorder *m_audioRecorder;
QString m_dossier;
};
class Main : public QWidget
{
Q_OBJECT
public:
Main();
private slots:
void restart();
private:
MainWindow *main;
};
#endif // LESSON_H
mainwindow.cpp
#include "mainwindow.h"
using namespace std;
MainWindow::MainWindow()
{
m_record = new QPushButton("Record");
m_recordPause = new QPushButton("Pause");
m_recordPause->setEnabled(false);
m_enableB = new QPushButton("Paste enabled");
m_recordState = new QLabel("Recording paused.");
m_recordState->setAlignment(Qt::AlignCenter);
m_enable = true;
QGridLayout *layout = new QGridLayout;
layout->addWidget(m_record,0,0,1,1);
layout->addWidget(m_recordPause,1,0,1,1);
layout->addWidget(m_enableB,2,0,1,1);
layout->addWidget(m_recordState,3,0,1,1);
setLayout(layout);
m_dossier = QFileDialog::getSaveFileName(this, "Save Audio File To:", QString(), "Audio (*.wav)");
m_audioRecorder = new QAudioRecorder(this);
m_audioRecorder->setOutputLocation(QUrl::fromLocalFile(m_dossier));
m_audioRecorder->setAudioInput(m_audioRecorder->defaultAudioInput());
QAudioEncoderSettings settings;
settings.setCodec("audio/amr");
settings.setSampleRate(16000);
settings.setBitRate(32);
settings.setQuality(QMultimedia::HighQuality);
settings.setEncodingMode(QMultimedia::ConstantQualityEncoding);
m_audioRecorder->setEncodingSettings(settings);
m_audio = new QMediaPlayer;
m_audio->setMedia(QUrl::fromLocalFile(m_dossier));
connect(m_recordPause, SIGNAL(clicked()), this, SLOT(togglePause()));
connect(m_record, SIGNAL(clicked()), this, SLOT(toggleRecord()));
connect(m_enableB, SIGNAL(clicked()), this, SLOT(setEnabled()));
}
void MainWindow::toggleRecord()
{
if (m_audioRecorder->state() == QMediaRecorder::StoppedState) {
m_record->setText("Stop");
m_recordPause->setEnabled(true);
m_audioRecorder->record();
m_recordState->setText("Recording.");
}
else
{
m_audioRecorder->stop();
m_audio->setMedia(QUrl::fromLocalFile(m_dossier));
emit end();
}
}
void MainWindow::togglePause()
{
if (m_audioRecorder->state() != QMediaRecorder::PausedState)
{
m_audioRecorder->pause();
m_recordPause->setText("Resume");
m_recordState->setText("Recording paused.");
}
else
{
m_audioRecorder->record();
m_recordPause->setText("Pause");
m_recordState->setText("Recording.");
}
}
void MainWindow::setEnabled()
{
if(m_enable)
{
m_enableB->setText("Paste disabled");
m_enable = false;
}
else
{
m_enableB->setText("Paste enable");
m_enable = true;
}
}
Main::Main()
{
main = new MainWindow();
QGridLayout *layout = new QGridLayout;
layout->addWidget(main,0,0,1,1);
setLayout(layout);
this->setFixedSize(200,200);
this->setWindowTitle("Notes");
connect(main, SIGNAL(end()), this, SLOT(restart()));
}
void Main::restart()
{
main = new MainWindow();
}
非常感谢您的帮助。
答
嗯,你需要了解指针如何在C和C++中工作。当你这样写:
void restart(Object *object)
{
object = new Object();
}
要复制的指针和指向新创建的对象将被分配到函数内部的“内部”拷贝变量。我想,你打算写的是改变外面的指针。
此外,如果您将指针改为外部,则需要确保旧对象被破坏。
话虽如此,这是一个非常糟糕的重置对象的方式。在我看来,你应该忘记这个概念有几个原因。首先,它的性能可能会很高。你基本上破坏然后再构造。例如,如果你有足够的可用内存,我会建议缓存默认值,但毕竟这是所有关于权衡的,不是吗?
如果你仍然坚持它,在这里不用你需要在初步实践应用代码:
您将需要申请下面的代码:
void restart(Object **object)
{
delete *object;
*object = new Object();
}
,然后调用你应该是这样的:
restart(&object);
尝试'void restart(Object ** object){delete * object; * object = new Object(); }'然后显然把它称为'restart(&object);'。 – lpapp 2014-10-26 22:50:06
工作感谢! – user3371807 2014-10-26 22:51:46