ifstream and ofstream.. save/read from memory?

The illustration would have been better, if I'd put repetitions into the loop rather than leaving my hard-coded value. Try the following with command line parameters 1024, 2048 and 4096. 1024 repeatitions of a string 1024 characters long fits into the large 1M buffer, 2048 repetitions requires one flush of the buffer. You should get the idea.

It is informative - this time 8-)

--------8<--------
#include <windows.h>
#include <iostream>
#include <fstream>
#include <vector>

int main(int argc,const char* argv[])
{
      if (argc != 2)
            return std::cerr << "Usage: " << *argv << " {repetitions}\n\n\tTry 1024,2048,4096",1;

      int repetitions = atoi(*++argv);

      // String to log
      std::vector<char> test(1025,'x');test[1024] = '\0';

// Normal logging
{
      DWORD start = GetTickCount();
      {
            std::ofstream fout("logfile_normal.txt");
            DWORD start = GetTickCount();
            for (int i = 0;i < repetitions;i++)
                  fout << &test[0];
            DWORD finish = GetTickCount();
            std::cout << "Normal run took " << finish-start << " millisecs\n";
      }
      DWORD finish = GetTickCount();
      std::cout << "Normal run took " << finish-start << " millisecs including ctor and dtor\n";
}

// Fast logging
{
      DWORD start = GetTickCount();
      const std::streamsize BufferSize = 1024*1024;      /* Buffer size of 1M */
      std::vector<char> buf(BufferSize);
      {
            std::ofstream fout("logfile_fast.txt");
            fout.rdbuf()->pubsetbuf(&buf[0],buf.size());
            DWORD start = GetTickCount();
            for (int i = 0;i < repetitions;i++)
                  fout << &test[0];
            DWORD finish = GetTickCount();
            std::cout << "Fast run took " << finish-start << " millisecs\n";
      }
      DWORD finish = GetTickCount();
      std::cout << "Fast run took " << finish-start << " millisecs including ctor and dtor\n";
}

}
--------8<--------

The library functions take ofstream (ifstream), not ostream (istream) references? If they take an ostream reference you can pass in an ostringstream and that will write into memory rather than out to the disk. You can then do whatever you want with the resulting string value in the buffer.

-bcl

it's taking ofstream and ifstream reference and I don't really want to handle the I/O myself.

Anthony_w: I'm using Visual C++ 6.0. I don't know much about the different stream class really and the MSDN help doesn't really talk too much about the std::stringstream.
Anyway, i've tried deriving a class from ofstream:


//copied from the other class that use ofstream
#if (_MSC_VER >= 1300) || defined(USE_NEW_IOSTREAMS)
#include <fstream>
using namespace std;
#else
#ifndef _INC_FSTREAM
#include <fstream.h>
#
#endif
#endif


#if !defined(AFX_MEMOFSTREAM_H__61B81A47_311F_4D1D_9F5C_B191931A7CF6__INCLUDED_)
#define AFX_MEMOFSTREAM_H__61B81A47_311F_4D1D_9F5C_B191931A7CF6__INCLUDED_

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

class memofstream : public ofstream  
{
public:
      memofstream();
      virtual ~memofstream();

private:      
      stringstream m_stringStream;
};

#endif // !defined(AFX_MEMOFSTREAM_H__61B81A47_311F_4D1D_9F5C_B191931A7CF6__INCLUDED_)



and when i compile it, the compiler complains:
syntax error : missing ';' before identifier 'm_stringStream'
'stringstream' : missing storage-class or type specifiers
'm_stringStream' : missing storage-class or type specifiers


so what did i do wrong?

btw, i believe i'm using:
#include<fstream.h>
not
#include <fstream>
using namespace std;


the reason is.. if i replace:

#if (_MSC_VER >= 1300) || defined(USE_NEW_IOSTREAMS)
#include <fstream>
using namespace std;
#else
#ifndef _INC_FSTREAM
#include <fstream.h>
#
#endif
#endif


with

#include <fstream>
using namespace std;


i got heaps of:    "'ofstream' : ambiguous symbol" error on the other file that use ofstream

std::stringstream is in the <sstream> header, so you need

#include <sstream>

at the top to make it compile.