#include <ifstream>
#include  <iosstream>
#include <dirent.h>
#include <string.h>

using namespace std;

int main(int argc, char* argv[])
{

//
//

  struct dirent* ent;
  DIR* dir = opendir(argv[1]); 
  char* fileName;

  //copying the files from the input dir to field subdirectories--10 in each
   while ((ent = readdir(dir)) != NULL)
   {
	if ((strcmp((char*)ent->d_name, ".") != 0) && (strcmp((char*)
	    ent->d_name, "..") != 0))
	{
	  fileName = ent->d_name;
	  cout << "input file name: " << fileName << endl;
	  cout << "fieldDirNames: " << fieldDirNames << endl;
	  char filePath[100];
	  strcpy((char*)filePath, fieldDirNames); 
         //fieldDirNames is part of the path of the output file
	  cout << "filePath: " << filePath << endl;
	  strcat((char*)filePath, "/");
	  strcat((char*)filePath, fileName);
	  cout << "output file path: " << filePath << endl;

	  ifstream inFile(fileName, ios::in|ios::binary);
	  cout << "opens the file" << endl;
	  long beg,end;
	  inFile.seekg(0, ios::beg);
	  cout << "puts the pointer at the beg of the file" << endl;
	  beg = inFile.tellg();   //*************RETURNS -1
	  cout << "beg: " << beg << endl;
	  inFile.seekg(0, ios::end);
	  end = inFile.tellg();
	  cout << "end: " << end << endl; //**************RETURNS -1
	  long size = (end - beg);
	  cout << "builds size var" << endl;
 	  cout << "size: " << size << endl;     // 0 is printed out
	  char* buffer = new char[size];
	  inFile.read( (char*) &buffer, size );
	  cout << "reads the file" << endl; 
	  ofstream outFile((char*)filePath, ios::out | ios::binary);
	  outFile.write((char*) &buffer[0], size);
	  delete[] buffer;
         }
     } 
}

char buffer[BUFSIZ];
...
Open both files (read and write)
...
do
{
    Read a bufferful (save the number of bytes read in nbyt)
    Write that buffer
} while (nbyt == BUFSIZ);

inFile.seekg(0, ios::end);  // position get-ptr 0 bytes from end
ios::pos_type size = inFile.tellg();  // get-ptr position is now same as file size