第3章 C++ I/O流技术

 

 

 

 

/*

  第3章 C++ I/O流技术
   3.1 I/O流类
   3.2 标准输入输出
   3.3 文件输入输出
   3.4 流的格式控制
   3.5 本章小结

*/


//  第3章 C++ I/O流技术
//   3.1 I/O流类 ------------------------------------------------------------------------------------------

//   3.2 标准输入输出 ------------------------------------------------------------------------------------------

// 35
#include <iostream>
int main(void)
{
  int i, j;
  std::cout << "请输入两个整数:\n";
  std::cin >> i;
  std::cin >> j;
  std::cout << "两整数之和等于:\n";
  std::cout << i + j;
  return 0;
}

// 35-36
#include <iostream>
using namespace std;
int main(void)
{
  int i, j;
  cout << "请输入两个整数" << endl;
  cin >> i >> j;
  cout << "两整数之和等于" << endl;
  cout << i + j << endl;
  return 0;
}

//   3.3 文件输入输出 ------------------------------------------------------------------------------------------

// 37 ，如无文件，会自动创建
#include <fstream>
#include <iostream>
using namespace std;
int main(void)
{
  ofstream wFileStream;
  wFileStream.open("x:\\水果.txt", ios::out | ios::app);
  if(!wFileStream)
  {
    cout << "打开文件失败" << endl;
    return 1;
  }
  wFileStream << "apple" << ' ' << "苹果" << endl;
  wFileStream << "banana" << ' ' << "香蕉" << endl;
  wFileStream << "grape" << ' ' << "葡萄" << endl;
  wFileStream.close();
  return 0;
}


// 36-37，如无文件，会显示打开文件失败。
#include <fstream>
#include <iostream>
using namespace std;
int main(void)
{
  ifstream rFileStream;
  rFileStream.open("d:\\水果.txt", ios::in);
  if(!rFileStream)
  {
    cout << "打开文件失败" << endl;
    return 1;
  }
  //读文件
  char eName[10], cName[10];
  rFileStream >> eName >> cName;
  cout << eName << ' ' << cName << endl;
  rFileStream >> eName >> cName;
  cout << eName << ' ' << cName << endl;
  rFileStream >> eName >> cName;
  cout << eName << ' ' << cName << endl;
  rFileStream.close();
  return 0;
}


// 38
#include <fstream>
#include <iostream>
using namespace std;
int main(void)
{
  ifstream rFileStream;
  rFileStream.open("d:\\水果.txt", ios::in | ios::binary);
  if(!rFileStream)
  {
    cout << "打开文件失败" << endl;
    return 1;
  }
  char c;
  while(!rFileStream.eof())
  {
    rFileStream.get(c);
    cout << c;
  }
  rFileStream.close();
  return 0;
}


// 39
#include <fstream>
#include <iostream>
using namespace std;
struct Student
{
  char name[8];
  int year;
};
int main(void)
{
  Student st;
  strcpy(st.name, "宋公明");
  st.year = 18;
  //
  ofstream wFileStream;
  wFileStream.open("d:\\student.txt", ios::out | ios::binary);
  if(!wFileStream)
  {
    cout << "打开文件失败" << endl;
    return 1;
  }
  wFileStream.write(reinterpret_cast < char * > (&st), sizeof(Student));
  wFileStream.close();
  //
  ifstream rFileStream;
  rFileStream.open("d:\\student.txt", ios::in | ios::binary);
  rFileStream.read(reinterpret_cast < char * > (&st), sizeof(Student));
  cout << st.name << "  " << st.year << endl;
  rFileStream.close();
  return 0;
}


// 39-40
#include <fstream>
#include <iostream>
using namespace std;
int main(void)
{
  ifstream rFileStream;
  rFileStream.open("d:\\水果.txt", ios::in);
  if(!rFileStream)
  {
    cout << "打开文件失败" << endl;
    return 1;
  }
  char str[30];
  rFileStream.getline(str, 30);
  cout << str;
  rFileStream.close();
  return 0;
}


// 40
#include <fstream>
#include <iostream>
using namespace std;
int main(void)
{
  fstream rwFileStream;
  rwFileStream.open("d:\\digit.txt", ios::in | ios::out | ios::binary | ios
    ::trunc);
  if(!rwFileStream)
  {
    cout << "打开文件失败" << endl;
    return 1;
  }
  for(char i = 0; i < 26; i++)
    rwFileStream << char('a' + i);
  //写入26个字母
  //
  rwFileStream.seekg(3, ios::beg); //定位到第3个字母处(从0索引)
  char c;
  rwFileStream.get(c);
  cout << c << endl; //打印出字符d
  rwFileStream.close();
  return 0;
}



//   3.4 流的格式控制 ------------------------------------------------------------------------------------------

// 42
#include <iostream>
using namespace std;
int main(void)
{
  cout.setf(ios::scientific | ios::uppercase);
  cout << 2006.5 << endl;
  //
  cout.setf(ios::floatfield, ios::fixed | ios::showpos);
  cout << 2006.5 << endl;
  //
  cout.setf(ios::showpos);
  cout << 2006.5 << endl;
  return 0;
}


//43
#include <iostream>
using namespace std;
int main(void)
{
  cout.width(20);
  cout << "hello" << endl; //右对齐输出hello,占20个字符
  //
  cout.precision(4);
  cout << 2006.526 << endl; //输出2007
  //
  cout.precision(5);
  cout << 2006.526 << endl; //输出2006.5
  //
  cout.precision(7); // 设置有效位数
  cout << 2006.526 << endl; //输出2006.526
  //
  cout.width(20);
  cout.fill('*');
  cout << "baby" << endl; //输出**************baby
  return 0;
}



// 44-45
#include <iostream>
#include <iomanip>
using namespace std;
int main(void)
{
  cout << setw(20) << "hello" << endl;
  cout << setprecision(4) << 2006.526 << endl;
  cout << setw(20) << setfill('*') << "baby" << endl;
  cout << scientific << 300.89 << endl;
  cout << oct << 9 << endl;
  cout << dec << showpos << 172 << endl;
  cout << noshowpos << 172 << endl;
  cout << boolalpha << true << endl;
  return 0;
}



// my test 。主要是为了测试浮点数的输出格式
#include <iostream>
//#include <iomanip>
using namespace std;
int main(void)
{
  double d(3.141592653589);
  cout << d << endl;  // 默认精度是六位有效数字
  cout.precision(20); // 设置有效位数20位
  cout << d << endl;

  cout.precision(3);  // 保留三位小数
  cout << fixed << d << endl; // fixed，浮点数以小数形式输出。有四舍五入功能
  
  return 0;
}



//   3.5 本章小结 ------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

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