C++的IO流

class Date
{
  friend ostream& operator << (ostream& out, const Date& date);
  friend istream& operator >> (istream& cin, Date& date);
  Date(int year = 1, int month = 1, int day = 1)
    :_year(year)
    ,_month(month)
    ,_day(day)
  {}
private:
  int _year;
  int _month;
  int _day;
};
ostream& operator << (ostream& out, const Date& date)
{
  out << date._year << " " << date._month << " " << date._day;
  return out;
}
istream& operator >> (istream& in, Date& date)
{
  in >> date._year >> date._month >> date._day;
  return in;
}

// 单个元素循环输入
while(cin>>a)
{
  // ...
}
// 多个元素循环输入
while(c>>a>>b>>c)
{
  // ...
}
// 整行接收
while(cin>>str)
{
  // ...
}

struct ServerInfo
{
  char _address[32];//地址
  int _port;//端口号
  Date _date;//日期
};
class ConfigManager
{
public:
  ConfigManager(const char* filename)
    :_filename(filename)
  {}
  //以二进制写文件
  void WriteBin(const ServerInfo& info)
  {
    ofstream ofs(_filename, ios_base::out | ios_base::binary);
    ofs.write((const 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，都使用一样的方式，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& date)
  ostream& operator << (ostream& out, const Date& date)
   */
  //以二进制读文件
  void ReadBin(ServerInfo& info)
  {
    ifstream ifs(_filename, ios_base::in | ios_base::binary);
    ifs.read((char*)&info, sizeof(info));
  }
  //以文本文件写文件
  void WriteText(const ServerInfo& info)
  {
    ofstream ofs(_filename);
    ofs << info._address << " " << info._port << " " << info._date;
  }
  //以文本文件读文件
  void ReadText(ServerInfo& info)
  {
    ifstream ifs(_filename);
    ifs >> info._address >> info._port >> info._date;
  }
private:
  string _filename; //文件名
};
int main()
{
  ServerInfo wInfo{ "192.0.0.1", 80, { 2022, 4, 10 } };
  //二进制读写
  ConfigManager cf_bin("Test.bin");
  cf_bin.WriteBin(wInfo);
  ServerInfo rInfo1;
  cf_bin.ReadBin(rInfo1);
  //文本文件读写
  ConfigManager cf_txt("Test.txt");
  cf_txt.WriteText(wInfo);
  ServerInfo rInfo2;
  cf_txt.ReadText(rInfo2);
  return 0;
}

int main()
{
  int n = 123456789;
  char s1[32];
  _itoa(n, s1, 10);
  char s2[32];
  sprintf(s2, "%d", n);
  char s3[32];
  sprintf(s3, "%f", n);
  return 0;
}

#include<sstream>
#include<iostream>
using namespace std;
int main()
{
  int a = 12345678;
  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 = " << sa << endl;
  cout << s.str() << endl; // str()方法：返回stringsteam中管理的string类型
  s.str(""); // 将stringstream底层管理string对象设置成""
  s.clear(); // 清空s, 不清空会转化失败
  double d = 12.34;
  s << d;
  s >> sa;
  cout << "sa = " << sa << endl;
  string sValue;
  sValue = s.str(); // str()方法：返回stringsteam中管理的string类型
  cout << sValue << endl;
  return 0;
}

int main()
{
  stringstream sstream;
  // 将多个字符串放入 sstream 中
  sstream << "first" << " " << "string,";
  sstream << " second string";
  cout << "strResult is: " << sstream.str() << endl;
  // 清空 sstream
  sstream.str("");
  sstream.clear();
  sstream << "third string";
  cout << "After clear, strResult is: " << sstream.str() << endl;
  return 0;
}

struct ChatInfo
{
  string _name; // 名字
  int _id;  // id
  Date _date;  // 时间
  string _msg;  // 聊天信息
};
int main()
{
  // 结构信息序列化为字符串
  ChatInfo winfo = { "张三", 135246, { 2022, 4, 10 }, "晚上一起看电影吧" };
  ostringstream oss;
  oss << winfo._name << " " << winfo._id << " " << winfo._date << " " << winfo._msg;
  string str = oss.str();
  cout << str << endl;
  // 我们通过网络这个字符串发送给对象，实际开发中，信息相对更复杂，一般会选用Json、xml等方式进行更好的支持字符串解析成结构信息。
  ChatInfo rInfo;
  istringstream iss(str);
  iss >> rInfo._name >> rInfo._id >> rInfo._date >> rInfo._msg;
  cout << "-------------------------------------------------------" << endl;
  cout << "姓名：" << rInfo._name << "(" << rInfo._id << ") ";
  cout << rInfo._date << endl;
  cout << rInfo._name << ":>" << rInfo._msg << endl;
  cout << "-------------------------------------------------------" << endl;
  return 0;
}