从C语言到C++_38(C++的IO流+空间适配器)STL六大组件联系（上）

int a;
cin >> a;

class Date
{
  friend ostream& operator << (ostream& out, const Date& d);
  friend istream& operator >> (istream& in, Date& d);
public:
  Date(int year = 1, int month = 1, int day = 1)
    :_year(year)
    , _month(month)
    , _day(day)
  {}
  operator bool()
  {   // 这里是随意写的，假设输入_year为0，则结束
    if (_year == 0)
    {
      return false;
    }
    else
    {
      return true;
    }
  }
private:
  int _year;
  int _month;
  int _day;
};
istream& operator >> (istream& in, Date& d)
{
  in >> d._year >> d._month >> d._day;
  return in;
}
ostream& operator << (ostream& out, const Date& d)
{
  out << d._year << "年" << d._month << "月" << d._day << "日";
  return out;
}
// C++ IO流，使用面向对象+运算符重载的方式
// 能更好的兼容自定义类型，流插入和流提取
int main()
{
  // 自动识别类型的本质--函数重载
  // 内置类型可以直接使用--因为库里面ostream类型已经实现了
  int i = 1;
  double j = 2.2;
  cout << i << endl;
  cout << j << endl;
  // 自定义类型则需要我们自己重载<< 和 >>
  Date d(2023, 1, 2);
  cout << d << endl;
  while (cin >> d)
  {
    cout << d << endl;;
  }
  return 0;
}

class Date
{
  friend ostream& operator<<(ostream& out, const Date& d);
  friend istream& operator>>(istream& in, Date& d);
public:
  Date(int year = 1, int month = 1, int day = 1)
    :_year(year)
    , _month(month)
    , _day(day)
  {}
  operator bool()
  {   // 这里是随意写的，假设输入_year为0，则结束
    if (_year == 0)
    {
      return false;
    }
    else
    {
      return true;
    }
  }
private:
  int _year;
  int _month;
  int _day;
};
istream& operator>>(istream& in, Date& d)
{
  in >> d._year >> d._month >> d._day;
  return in;
}
ostream& operator<<(ostream& out, const Date& d)
{
  out << d._year << " " << d._month << " " << d._day; // 文本读写先用空格分割，不然再从文件读就错了
  return out;
}
 
struct ServerInfo
{
  char _address[32];
  int _port;
  Date _date;
};
struct ConfigManager
{
public:
  ConfigManager(const char* filename)
    :_filename(filename)
  {}
  void WriteBin(const ServerInfo& info)
  {
    ofstream ofs(_filename, ios_base::out | ios_base::binary); // 两种状态
    ofs.write((const char*)&info, sizeof(info));
  }
  void ReadBin(ServerInfo& info)
  {
    ifstream ifs(_filename, ios_base::in | ios_base::binary);
    ifs.read((char*)&info, sizeof(info));
  }
  // C++文件流的优势就是可以对内置类型和自定义类型，都适用
  // 一样的方式，去流插入和流提取数据
  // 当然这里自定义类型Date需要重载>> 和 <<
  // istream& operator >> (istream& in, Date& d)
  // ostream& operator << (ostream& out, const Date& d)
  void WriteText(const ServerInfo& info)
  {
    ofstream ofs(_filename);
    ofs << info._address << " " << info._port << " " << info._date;
  }
  void ReadText(ServerInfo& info)
  {
    ifstream ifs(_filename);
    ifs >> info._address >> info._port >> info._date;
  }
private:
  string _filename; // 配置文件
};
 
int main()
{
  ServerInfo winfo = { "777.6.5.4", 80, { 2023, 5, 4 } };
  // 二进制读写
  ConfigManager cf_bin("test.bin");
  cf_bin.WriteBin(winfo);
  ServerInfo rbinfo;
  cf_bin.ReadBin(rbinfo);
  cout << rbinfo._address << " " << rbinfo._port << " " << rbinfo._date << endl;
 
  // 文本读写
  ConfigManager cf_text("test.text");
  cf_text.WriteText(winfo);
  ServerInfo rtinfo;
  cf_text.ReadText(rtinfo);
  cout << rtinfo._address << " " << rtinfo._port << " " << rtinfo._date << endl;
  return 0;
}

#include<sstream>
int main()
{
  int a = 7654321;
  string sa;
  // 将一个整形变量转化为字符串，存储到string类对象中
  stringstream s;
  s << a;
  s >> sa;
  cout << sa << endl;
  // clear()
  // 注意多次转换时，必须使用clear将上次转换状态清空掉
  // stringstreams在转换结尾时(即最后一个转换后),会将其内部状态设置为badbit
  // 因此下一次转换是必须调用clear()将状态重置为goodbit才可以转换
  // 但是clear()不会将stringstreams底层字符串清空掉
 
  // s.str("");
  // 将stringstream底层管理string对象设置成"", 
  // 否则多次转换时，会将结果全部累积在底层string对象中
 
  s.str("");
  s.clear(); // 清空s, 不清空会转化失败
  double d = 12.34;
  s << d;
  s >> sa;
  string sValue;
  sValue = s.str(); // str()方法：返回stringsteam中管理的string类型
  cout << sValue << endl;
  return 0;
}