C++: CSV Data Manipulation

#include <map>
#include <vector>
#include <iostream>
#include <fstream>
#include <utility>
#include <functional>
#include <string>
#include <sstream>
#include <algorithm>
#include <cctype>

class CSV
{
public:
	CSV(void) : m_nCols( 0 ), m_nRows( 0 )
	{}

	bool open( const char* filename, char delim = ',' )
	{
		std::ifstream file( filename );

		clear();
		if ( file.is_open() )
		{
			open( file, delim );
			return true;
		}

		return false;
	}

	void open( std::istream& istream, char delim = ',' )
	{
		std::string         line;

		clear();
		while ( std::getline( istream, line ) )
		{
			unsigned int nCol = 0;
			std::istringstream    lineStream(line);
			std::string           cell;

			while( std::getline( lineStream, cell, delim ) )
			{
				m_oData[std::make_pair( nCol, m_nRows )] = trim( cell );
				nCol++;
			}
			m_nCols = std::max( m_nCols, nCol );
			m_nRows++;
		}
	}

	bool save( const char* pFile, char delim = ',' )
	{
		std::ofstream ofile( pFile );
		if ( ofile.is_open() )
		{
			save( ofile );
			return true;
		}
		return false;
	}

	void save( std::ostream& ostream, char delim = ',' )
	{
		for ( unsigned int nRow = 0; nRow < m_nRows; nRow++ )
		{
			for ( unsigned int nCol = 0; nCol < m_nCols; nCol++ )
			{
				ostream << trim( m_oData[std::make_pair( nCol, nRow )] );
				if ( (nCol+1) < m_nCols )
				{
					ostream << delim;
				}
				else
				{
					ostream << std::endl;
				}
			}
		}
	}

	void clear()
	{
		m_oData.clear();
		m_nRows = m_nCols = 0;
	}

	std::string& operator()( unsigned int nCol, unsigned int nRow )
	{
		m_nCols = std::max( m_nCols, nCol+1 );
		m_nRows = std::max( m_nRows, nRow+1 );
		return m_oData[std::make_pair(nCol, nRow)];
	}

	inline unsigned int GetRows() { return m_nRows; }
	inline unsigned int GetCols() { return m_nCols; }

private:
	// trim string for empty spaces in begining and at the end
	inline std::string &trim(std::string &s) 
	{

		s.erase(s.begin(), std::find_if(s.begin(), s.end(), std::not1(std::ptr_fun<int, int>(std::isspace))));
		s.erase(std::find_if(s.rbegin(), s.rend(), std::not1(std::ptr_fun<int, int>(std::isspace))).base(), s.end());
		return s;
	}

private:
	std::map<std::pair<unsigned int, unsigned int>, std::string> m_oData;

	unsigned int    m_nCols;
	unsigned int    m_nRows;
};


int main()
{
	CSV oCSV;

	oCSV.open( "test_in.csv" );
	oCSV( 0, 0 ) = "Column0";
	oCSV( 1, 1 ) = "100";
	oCSV( 2, 2 ) = "200";
	oCSV( 3, 3 ) = "300";
	oCSV( 4, 4 ) = "400";
	oCSV.save( "test_out.csv" );
	return 0;
}

Output (in test_out.csv):