6.C++ Standard Library

The Codes:

 

// 6. C++ Standard Library

/********************************************
1. Input/Output with files
*/


// basic file operations
#include <iostream>
#include <fstream>
using namespace std;

int main () 
{
  ofstream myfile;
  myfile.open ("example.txt"); //如无些文件，新建一个。在程序文件的同一目录下
  myfile << "Writing this to a file.\n";
  myfile.close();

  return 0;
}


// writing on a text file
#include <iostream>
#include <fstream>
using namespace std;

int main () 
{
  ofstream myfile("example.txt");
  if(myfile.is_open())
  {
    myfile<<"This is a line.\n";
    myfile<<"This is another line.\n";
    myfile.close();
  }
  else cout << "Unable to open file";

  return 0;
}


// reading a text file
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main () 
{
  string line;
  ifstream myfile("example.txt");
  if(myfile.is_open())
  {
    while(! myfile.eof() )
    {
      getline(myfile,line);
      cout << line << endl;
    }
    myfile.close();
  }
  else cout << "Unable to open file";

  return 0;
}



// obtaining file size
#include <iostream>
#include <fstream>
using namespace std;

int main () 
{
  long begin,end;
  ifstream myfile("example.txt");
  begin = myfile.tellg(); // 取得第一个光标位置
  myfile.seekg(0,ios::end);
  end = myfile.tellg(); // 取得最后一个光标位置
  myfile.close();
  cout << "size is: " << (end-begin) << " bytes.\n";

  return 0;
}




// reading a complete binary file
#include <iostream>
#include <fstream>
using namespace std;

ifstream::pos_type size;
char * memblock;

int main () 
{
  ifstream file("example.bin",ios::in|ios::binary|ios::ate);
  if(file.is_open())
  {
    size=file.tellg();
    memblock=new char [size];
    file.seekg(0,ios::beg);
    file.read(memblock,size);
    file.close();
    
    cout << "the complete file content is in memory";
    
    delete[] memblock;
  }
  else cout << "Unable to open file";
  return 0;
}

 

 

 

 

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