退出qt5时程序崩溃

Question

我将QApplication::quit();添加到两个if语句中，这样当用户单击' cancel‘或'x’时，程序就会结束；然而，一旦单击cancel或x，程序就会崩溃，程序会出现问题。我不知道它为什么总是崩溃。我在main.cpp文件中添加了这段代码。

头文件：

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QString>

class SentenceProcessor {
  public:
    int getWordNumber(QString sentence);
    int getVowelNumber(QString sentence);
    bool isReversible(QString sentence);
    QString wordsReversed(QString sentence);
    QString formatSentence(QString sentence);
};

#endif // MAINWINDOW_H

实施文件：

#include "mainwindow.h"
#include <QString>
#include <QStringList>

int SentenceProcessor::getWordNumber(QString sentence) {
  QStringList list = sentence.split(" ");
  int len = 0;
  foreach(QString str, list) {
    len++;
  }
  return len;
}

int SentenceProcessor::getVowelNumber(QString sentence) {
  int count = 0;
  int len = sentence.size();
  for (int i = 0; i < len; i++) {
    if (sentence.data()[i] == 'a' || sentence.data()[i] == 'A' || sentence.data()[i] == 'e' || sentence.data()[i] == 'E' || sentence.data()[i] == 'i' ||
      sentence.data()[i] == 'I' || sentence.data()[i] == 'o' || sentence.data()[i] == 'O' || sentence.data()[i] == 'u' || sentence.data()[i] == 'U') {
      count++;
    }
  }

  return count;

}

bool SentenceProcessor::isReversible(QString sentence) {
  QStringList list1 = sentence.split(" ");
  QStringList list2;
  int count = 0;
  bool reversible;
  foreach(QString str, list1) {
    list2.prepend(str);
  }
  for (int i = 0; i < list1.size(); i++) {
    if (QString::compare(list1[i], list2[i], Qt::CaseInsensitive) == 0) {
      count++;
    }
  }
  if (count == list1.size()) {
    reversible = true;
  } else {
    reversible = false;
  }
  return reversible;
}

QString SentenceProcessor::wordsReversed(QString sentence) {
  QStringList list1 = sentence.split(" ");
  QStringList list2;
  foreach(QString str, list1) {
    list2.prepend(str);
  }
  QString reversed = list2.join(" ");

  return reversed;
}

QString SentenceProcessor::formatSentence(QString sentence) {
  sentence.data()[0] = sentence.data()[0].toUpper();
  int len = sentence.length();
  if (sentence.data()[len - 1] != '.') {
    sentence.append('.');
  }
  return sentence;
}

用于测试的Main.cpp文件:在这个文件中，我添加了QApplication::quit();

#include "mainwindow.h"
#include <QApplication>
#include <QString>
#include <QStringList>
#include <QTextStream>
#include <QInputDialog>
#include <QMessageBox>


int main(int argc, char * argv[]) {
   QApplication app(argc, argv);
  QMessageBox::StandardButton response;
  response = QMessageBox::question(0, "Ready for input", "Are you ready to enter a sentence?", QMessageBox::Yes | QMessageBox::No);

  while (response == QMessageBox::Yes) {
    SentenceProcessor s1;
    bool ok;
    QString text = QInputDialog::getText(0, "Sentence Processor", "Enter sentence", QLineEdit::Normal, 0, &ok);
    QStringList list = text.split(" ");

    if (ok) {
      while (list.size() < 2) {
        QMessageBox::information(0, "Error", "You need to enter at least two words");
        text = QInputDialog::getText(0, "Sentence Processor", "Enter sentence", QLineEdit::Normal, 0, &ok);
        if (!ok) {
            QApplication::quit();
        }else{
             list = text.split(" ");
        }
      }

      QString numWords = QString::number(s1.getWordNumber(text));
      QString numVowels = QString::number(s1.getVowelNumber(text));
      bool reversible = s1.isReversible(text);
      QString wordsReverse = s1.wordsReversed(text);
      QString senFormat = s1.formatSentence(text);
      QString reversibleText;
      if (reversible == false) {
        reversibleText = "Your sentence is not reversible";
      } else {
        reversibleText = "Your sentence is reversible";
      }

      QMessageBox::information(0, "Sentence Processing", "Your sentence: " + text + "\n" +
        "The number of words in your sentence is: " + numWords + "\n The number of vowels in your sentence: " +
        numVowels + "\n" + reversibleText + "\n" + "Your sentence reversed is: " + wordsReverse + "\n" +
        "Your sentence formatted is: " + senFormat);

      response = QMessageBox::question(0, "Another Input", "Would you like to enter another sentence?", QMessageBox::Yes | QMessageBox::No);
    }else{
        QApplication::quit();
   }
  }
  return app.exec();
}

Answer 1

造成崩溃的原因可能是在代码中使用QApplication::quit();，甚至在调用应用程序exec()之前。看起来，您假设quit()是函数的出口点。事实并非如此。只有return或作用域结束是任何函数(包括main() )的退出点。您应该使用return (并返回0或一些错误代码，如1或-1，这取决于您自己)，而不是所有的QApplication::quit()调用，然后它可能会像您预期的那样工作。

由于您实际上没有使用应用程序事件循环，所以很可能应该删除app.exec();。只需使用return 0;即可。使用app.exec()，您的应用程序将永远不会完成。

顺便说一句，这种设计Qt代码的方法是错误的。理想情况下，应该在应用程序的事件循环运行时执行代码。从调用exec()开始。但是，考虑到消息框有自己的事件循环，您的代码最终可能会正常工作。但这绝对是一种错误的Qt应用程序方式。总的来说，您应该研究Qt应用程序中的事件循环是什么以及它是如何工作的。你的代码看上去好像毫无头绪。