.
.
.
std::auto_ptr<std::ifstream> *keypointsIn_pt ;
keypointsIn_pt = std::auto_ptr<std::ifstream>(new std::ifstream(keypointsFilename.c_str(),std::ios::binary)) ;
while( !keypointsIn_pt->eof() ) {....}
.
.
.

#include<vector>
#include<math.h>
#include"sift.hpp"
#include"sift.h"
#include"sift.ipp"
#include"sift-conv.h"
#include<algorithm>
#include<iostream>
#include<memory>
#include<sstream>
#include<cassert>
.
.
.
	Sift::Keypoint* Sift::ReadKeys(FILE *fp)
	{
		Keypoints keypoints ;
		std::string keypointsFilename;
		// If a keypoint file is provided, then open it now 
		std::auto_ptr<std::ifstream> keypointsIn_pt ;
		keypointsIn_pt = std::auto_ptr<std::ifstream>
			(new std::ifstream(keypointsFilename.c_str(),std::ios::binary)) ;
		
		while( !keypointsIn_pt->eof() ) {
			VL::float_t x,y,sigma,th ;
			
			// read x, y, sigma and th from the beginning of the line 
			(*keypointsIn_pt) 
				>> x
				>> y
				>> sigma
				>> th ;
			
			// skip the rest of the line 
			(*keypointsIn_pt).ignore(numeric_limits<streamsize>::max(),'\n') ;
			
			// break the loop if end of file reached 
			if( keypointsIn_pt->eof() ) break ;
			
			//trhow an error if something wrong 
			if( ! keypointsIn_pt->good() ) 
				VL_THROW("Error reading keypoints file.") ;
			
			// compute integer components 
			VL::Sift::Keypoint key 
				= sift.getKeypoint(x,y,sigma) ;
			
			Keypoints::value_type entry ;
			entry.first  = key ;
			entry.second = th ;
			keypoints.push_back(entry) ;
		}
		return ???;
	}

    std::auto_ptr<std::ifstream> *keypointsIn_pt ; //keypointsIn_pt is  pointer to an auto_ptr
    keypointsIn_pt = std::auto_ptr<std::ifstream>(new std::ifstream(keypointsFilename.c_str(),std::ios::binary)) ; // Error: can't assign an auto_ptr value to keypointsIn_pt

    std::auto_ptr<std::ifstream> keypointsIn_pt ; //keypointsIn_pt is an auto_ptr
    keypointsIn_pt = std::auto_ptr<std::ifstream>(new std::ifstream(keypointsFilename.c_str(),std::ios::binary)) ; // OK: Assign an auto_ptr value to keypointsIn_pt.