How to use boost::transform_iterator to iterate over modifed std::map values?
- by Frank
I have an std::map, and I would like to define an iterator that returns modified values. Typically, a std::map<int,double>::iterator iterates over std::pair<int,double>, and I would like the same behavior, just the double value is multiplied by a constant.
I tried it with boost::transform_iterator, but it doesn't compile:
#include <map>
#include <boost/iterator/transform_iterator.hpp>
#include <boost/functional.hpp>
typedef std::map<int,double> Map;
Map m;
m[100] = 2.24;
typedef boost::binder2nd< std::multiplies<double> > Function;
typedef boost::transform_iterator<Function,
Map::value_type*> MultiplyIter;
MultiplyIter begin =
boost::make_transform_iterator(m.begin(),
Function(std::multiplies<double>(), 4));
// now want to similarly create an end iterator
// and then iterate over the modified map
The error is:
error: conversion from 'boost
::transform_iterator<
boost::binder2nd<multiplies<double> >, gen_map<int, double>::iterator
, boost::use_default, boost::use_default
>' to non-scalar type 'boost::transform_iterator<
boost::binder2nd<multiplies<double> >, pair<const int, double> *
, boost::use_default, boost::use_default
>' requested
What is gen_map and do I really need it?
I adapted the transform_iterator tutorial code from here to write this code ...
