id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
5825	constructing function_input_iterator without consuming an item	Maximiliano Garrone ten Brink <maximiliano@…>	Dean Michael Berris	"The only constructor for function_input_iterator always consumes an item from the generator. This makes it difficult to define a past-the-end iterator.

The first example given in http://www.boost.org/doc/libs/1_47_0/libs/iterator/doc/function_input_iterator.html calls rand() 11 times instead of the 10 expected. This can be a more serious problem when, for example, reading a file, as shown in the following program:


{{{
#include <string>
#include <fstream>
#include <iostream>
#include <algorithm>

#include <boost/iterator/function_input_iterator.hpp>

static const std::string filename( ""test.txt"" );

struct generator {
    typedef int result_type;
    generator() : in( filename ) {}

    result_type operator() () {
		result_type ret;
		in >> ret;
		return ret;
    }

	std::ifstream in;
};

int main(int argc, char * argv[]) {
	std::ofstream out( filename );
	out << 0 << std::endl
		<< 1 << std::endl
		<< 2 << std::endl
		<< 3 << std::endl;

    generator f;
    std::copy(
            boost::make_function_input_iterator(f, 0),
            boost::make_function_input_iterator(f, 3),
            std::ostream_iterator<int>(std::cout, "" "")
        ); // ""1 2 3"" is shown on cout, instead of ""0 1 2""
    return 0;
}
}}}

A possible solution could be adding a different constructor to function_input_iterator specifically to represent a past-the-end iterator."	Bugs	closed	To Be Determined	iterator	Boost 1.47.0	Showstopper	fixed	function_input_iterator past-the-end	mikhailberis@…