Boost spirit parser of Fortran printed doubles

Question

I am using num_list3.cpp from Boost Spirit examples. I am testing the variety of the double types it can parse. I used the following list:

1.2,0.2
.2,5.
1.e+23,.23E4
0e+10
1.3D+3

I noticed that it fails on parsing the last number 1.3D+3.

How could I set D as an exponent prefix of a double?

Answer 1

You can easily do that with Boost.Spirit. You just need to instantiate a real_parser with a custom policy that takes care of the "d|D" prefix. It could be as simple as:

template <typename Type>
struct fortran_policy : qi::real_policies<Type>
{
    template <typename Iterator>
    static bool parse_exp(Iterator& first, const Iterator& last)
    {
        if (first == last || (*first != 'e' && *first != 'E' && *first != 'd' && *first != 'D'))
            return false;
        ++first;
        return true;
    }
};

Then you would simply need to use:

qi::real_parser<double,fortran_policy<double>> double_;

without needing to change anything else(although that semantic action seems rather unnecessary).

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