c++ - c中第二次读取文件时程序崩溃

Question

使用c++文件流第二次读取文件时程序崩溃

嗨，伙计，我正在尝试构建一个允许用户输入所有数据的 Qt Gui 应用程序并使用 C++ 文件流将其写入文件。当我尝试从文件中读回所有数据时，它第一次工作正常，但是当我关闭应用程序并再次尝试读取它时，我的应用程序崩溃了。我尽力修复它，但找不到任何解决方案。任何人都可以帮助我。这是我从文件中读取数据的源代码。

void Form::OpenSlot()
{
    OpenDialog = new QFileDialog();
    FilePath = OpenDialog->getOpenFileName(this,"Open",AppDir,"Binary Files(*.bin)");
    QString strID, strName, strSex, strSalary, strHour, strRate, strTotal;
    int row = 0;
    Employee *emp = NULL;

    if(!FilePath.isEmpty())
    {
        isNew = false;
        fstream fout(FilePath.toStdString().c_str(),ios::binary|ios::in);

        if(fout.fail())
        {
            msg->setText("Error reading file.\nWrong format.");
            msg->show();
            fout.close();
            return;
        }

        fout.seekg(0,ios::end);
        row = (int)(fout.tellg()/sizeof(Employee));
        fout.seekg(0,ios::beg);
        emp = new Employee[row];
        fout.read((char*)emp,row*sizeof(Employee));
        fout.close();

        for(int i=0;i<row;i++)
        {
            DisplayTable->removeRow(i);
        }

        for(int i=0;i<row;i++)
        {
            strID = QString::number((emp+i)->getID());
            strName = QString::fromStdString((emp+i)->getName());
            strSex = QString::fromStdString((emp+i)->getSex());
            strSalary = QString::number((emp+i)->getSalary());
            strHour = QString::number((emp+i)->getHour());
            strRate = QString::number((emp+i)->getRate());
            strTotal = QString::number((emp+i)->getTotal());

            DisplayTable->insertRow(i);

            DisplayTable->setItem(i,0,new QTableWidgetItem(strID));
            DisplayTable->setItem(i,1,new QTableWidgetItem(strName));
            DisplayTable->setItem(i,2,new QTableWidgetItem(strSex));
            DisplayTable->setItem(i,3,new QTableWidgetItem(strSalary));
            DisplayTable->setItem(i,4,new QTableWidgetItem(strHour));
            DisplayTable->setItem(i,5,new QTableWidgetItem(strRate));
            DisplayTable->setItem(i,6,new QTableWidgetItem(strTotal));
        }
    }
    else
    {
        msg->setText("Can not find path");
        msg->show();
    }

    delete []emp;

这是将数据写入文件的源代码。

void Form::SaveSlot()
{
    int row = DisplayTable->rowCount();
    // Write Data to file
    if(!isNew)
    {
        fstream fin(FilePath.toStdString().c_str(),ios::binary|ios::out);
        Employee *emp = new Employee[row];

        for(int i=0;i<row;i++)
        {
             emp->setID(DisplayTable->item(i,0)->text().toInt());
             emp->setName(DisplayTable->item(i,1)->text().toStdString());
             emp->setSex(DisplayTable->item(i,2)->text().toStdString());
             emp->setSalary(DisplayTable->item(i,3)->text().toFloat());
             emp->setHour(DisplayTable->item(i,4)->text().toInt());
             emp->setRate(DisplayTable->item(i,5)->text().toFloat());
             emp->setTotal(DisplayTable->item(i,6)->text().toFloat());
             fin.write((char*)&emp,sizeof(Employee));
        }
        fin.close();
    }
    else
    {
        SaveDialog = new QFileDialog();
        FilePath = SaveDialog->getSaveFileName(this,"Save",AppDir,"BinaryFile(*.bin)");

        if(FilePath.isEmpty())
            return;

        fstream fin(FilePath.toStdString().c_str(),ios::binary|ios::out);
        Employee *emp = new Employee[row];

        for(int i=0;i<row;i++)
        {
             (emp+i)->setID(DisplayTable->item(i,0)->text().toInt());
             (emp+i)->setName(DisplayTable->item(i,1)->text().toStdString());
             (emp+i)->setSex(DisplayTable->item(i,2)->text().toStdString());
             (emp+i)->setSalary(DisplayTable->item(i,3)->text().toFloat());
             (emp+i)->setHour(DisplayTable->item(i,4)->text().toInt());
             (emp+i)->setRate(DisplayTable->item(i,5)->text().toFloat());
             (emp+i)->setTotal(DisplayTable->item(i,6)->text().toFloat());
        }

        fin.write((char*)emp,row*sizeof(Employee));
        fin.close();
    }
}

这是 Employee 类的原型(prototype)。

class Employee
{
public:
    Employee();
    Employee(Employee &emp);
    Employee(int id,string name,string sex,float salary,int hour,float rate,float total);
    void setID(int id);
    void setName(string name);
    void setSex(string sex);
    void setSalary(float salary);
    void setHour(int hour);
    void setRate(float rate);
    void setTotal(float total);
    int getID();
    string getName();
    string getSex();
    float getSalary();
    int getHour();
    float getRate();
    float getTotal();
private:
    int m_id;
    string m_name;
    string m_sex;
    float m_salary;
    int m_hour;
    float m_rate;
    float m_total;
};

Answer 1

一个可能的问题:

fstream fout(FilePath.toStdString().c_str(),ios::binary|ios::in);

这里 FilePath.toStdString() 返回一个临时的 std::string，然后你调用 c_str() 并得到一个指向它的指针数据。然后临时字符串被销毁，你将悬空指针发送给 fstream 构造函数!你可以这样做:

string filePathStr = FilePath.toStdString();
fstream fout(filePathStr.c_str(),ios::binary|ios::in);

或者直接使用QFile。它需要一个 QString 作为文件路径。

---

此外，您不会在 void Form::SaveSlot() 上删除 emp:

Employee *emp = new Employee[row];

(不会导致您的崩溃，但您可能希望避免内存泄漏。)