ErrorHandler.h

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#ifndef _ERRORHANDLER_H
#define _ERRORHANDLER_H

#include <iostream>
#include <string>
#include <vector>

template <typename Iterator>
struct ErrorHandler
{
    template <typename, typename, typename>
    struct result 
    { 
        typedef void type; 
    };

    ErrorHandler(Iterator first, Iterator last)
      : first(first), last(last) {}

    template <typename Message, typename What>
    void operator()(
        Message const& message,
        What const& what,
        Iterator err_pos) const
    {
        int line;
        Iterator line_start = get_pos(err_pos, line);
        if (err_pos != last)
        {
            std::cout << message << what << " line " << line << ':' << std::endl;
            std::cout << get_line(line_start) << std::endl;
            for (; line_start != err_pos; ++line_start)
                std::cout << ' ';
            std::cout << '^' << std::endl;
        }
        else
        {
            std::cout << "Unexpected end of file. ";
            std::cout << message << what << " line " << line << std::endl;
        }
    }

    Iterator get_pos(Iterator err_pos, int& line) const
    {
        line = 1;
        Iterator i = first;
        Iterator line_start = first;
        while (i != err_pos)
        {
            bool eol = false;
            if (i != err_pos && *i == '\r') // CR
            {
                eol = true;
                line_start = ++i;
            }
            if (i != err_pos && *i == '\n') // LF
            {
                eol = true;
                line_start = ++i;
            }
            if (eol)
                ++line;
            else
                ++i;
        }
        return line_start;
    }

    std::string get_line(Iterator err_pos) const
    {
        Iterator i = err_pos;
        // position i to the next EOL
        while (i != last && (*i != '\r' && *i != '\n'))
            ++i;
        return std::string(err_pos, i);
    }

    Iterator first; 
    Iterator last; 
    std::vector<Iterator> iters; 
};

#endif