basic_istream::gcount

To obtain the number of bytes read.

  streamsize gcount() const;
  

Use the function gcount() to obtain the number of bytes read by the last unformatted input function called by that object.

Returns an int type count of the bytes read.

#include <iostream>
#include <fstream>

const SIZE = 4;

struct stArray {

   int index;

   double dNum;

};

int main()

{ 

using namespace std;

   ofstream fOut("test");

   if(!fOut.is_open()) 

      {cout << "can't open out file"; return 1;}

   stArray arr;

   short i; 

   for(i = 1; i < SIZE+1; i++) 

   {

      arr.index = i;

      arr.dNum = i *3.14;

      fOut.write((char *) &arr, sizeof(stArray));

   }

   fOut.close();

   stArray aIn[SIZE];

   ifstream fIn("test");

   if(!fIn.is_open()) 

      {cout << "can't open in file"; return 2;}

   long count =0;

   for(i = 0; i < SIZE; i++) 

   {       fIn.read((char *) &aIn[i], sizeof(stArray));

   count+=fIn.gcount();

   }

   cout << count << " bytes read " << endl;

   cout << "The size of the structure is " 

      << sizeof(stArray) << endl;

   for(i = 0; i < SIZE; i++)

   cout << aIn[i].index << " " << aIn[i].dNum 

      << endl;

   fIn.close();

   return 0;

}

Result:

  48 bytes read 
  The size of the structure is 12
  1 3.14
  2 6.28
  3 9.42
  4 12.56