该博文的目的是对C++类的概念的理解.

设计CBook类

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class CBook {
public:
  CBook() {}
  ~CBook() {}
  CBook(char *cName, char *clsbn, char *cPrice, char *cAuthor);

public:
  void WriteData();
  void DeleteDate(int iCount);
  void GetBookFromFile(int iCount);

protected:
  char m_cName[NUM1];
  char m_clsbn[NUM1];
  char m_cPrice[NUM2];
  char m_cAuthor[NUM2];
};

拷贝构造函数函数的实现

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CBook::CBook(char *cName, char *clsbn, char *cPrice, char *cAuthor) {
  strncpy(m_cName, cName, NUM1);
  strncpy(m_clsbn, clsbn, NUM1);
  strncpy(m_cPrice, cPrice, NUM2);
  strncpy(m_cAuthor, cAuthor, NUM2);
}

添加模块

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void CBook::WriteData() {
  ofstream ofile;
  ofile.open("book.dat", ios::binary | ios::app);
  try {
    ofile.write(m_cName, NUM1);
    ofile.write(m_clsbn, NUM1);
    ofile.write(m_cPrice, NUM2);
    ofile.write(m_cAuthor, NUM2);
  } catch (...) {
    throw "file error occurred ";
    ofile.close();
  }
  ofile.close();
}

删除模块

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void CBook::DeleteDate(int iCount) {
  long respos;
  int iDataCount = 0; 
  fstream file;
  fstream tmpfile;
  ofstream ofile;
  char cTempBuf[NUM1 + NUM1 + NUM2 + NUM2];
  file.open("book.dat", ios::binary | ios::in | ios::out);
  tmpfile.open("temp.dat", ios::binary | ios::in | ios::out | ios::trunc);
  file.seekg(0, ios::end);
  respos = file.tellg();
  iDataCount = respos / (NUM1 + NUM1 + NUM2 + NUM2);
  if (iCount < 0 && iCount > iDataCount) {
    throw "Input number error";
  } else {
    file.seekg((iCount) * (NUM1 + NUM1 + NUM2 + NUM2), ios::beg);
    for (int j = 0; j < (iDataCount - iCount); j++) {
      memset(cTempBuf, 0, NUM1 + NUM1 + NUM2 + NUM2);
      file.read(cTempBuf, NUM1 + NUM1 + NUM2 + NUM2);
      tmpfile.write(cTempBuf, NUM1 + NUM1 + NUM2 + NUM2);
    }
    file.close();
    tmpfile.seekg(0, ios::beg);
    ofile.open("book.dat");
    ofile.seekp((iCount - 1) * (NUM1 + NUM1 + NUM2 + NUM2), ios::beg);
    for (int i = 0; i < (iDataCount - iCount); i++) {
      memset(cTempBuf, 0, NUM1 + NUM1 + NUM2 + NUM2);
      tmpfile.read(cTempBuf, NUM1 + NUM1 + NUM2 + NUM2);
      ofile.write(cTempBuf, NUM1 + NUM1 + NUM2 + NUM2);
    }
  }
  tmpfile.close();
  ofile.close();
  remove("temp.dat");
}

浏览模块

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void CBook::GetBookFromFile(int iCount) {
  char cName[NUM1];
  char clsbn[NUM1];
  char cPrice[NUM2];
  char cAuthor[NUM2];
  ifstream ifile; //这里创建了一个ifile输入流
  ifile.open("book.dat", ios::binary);
  try {
    ifile.seekg(iCount * (NUM1 + NUM1 + NUM2 + NUM2), ios::beg);
    ifile.read(cName, NUM1);
    // char * strncpy ( char * destination, const char * source, size_t num );
    if (ifile.tellg() > 0)
      strncpy(m_cName, cName, NUM1);
    ifile.read(clsbn, NUM1);
    if (ifile.tellg() > 0)
      strncpy(m_clsbn, clsbn, NUM1);
    ifile.read(cPrice, NUM2);
    if (ifile.tellg() > 0)
      strncpy(m_cPrice, cPrice, NUM2);
    ifile.read(cAuthor, NUM2);
    if (ifile.tellg() > 0)
      strncpy(m_cAuthor, cAuthor, NUM2);
  } catch (...) {
    throw "file error occurred";
    ifile.close();
  }
  ifile.close();
}

待续

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