Re: spirit list_p example

From: Larry Knain (yg-boost-users_at_[hidden])
Date: 2003-09-01 17:27:41

Thanks Hartmut.

I inserted the code change you suggested and it picks up the 2 but there is no
indication of the "missing" list element.  I'll do some more reading and see what
I can come up with.  (I have a number of CSV files created by various
spreadsheets and DB programs that I need to read that have "missing" list
items and was trying for a more elegant solution in Spirit. I have done this with
the tokenizer by keeping the delimiter tokens.)

HartmutKaiser_at_[hidden] wrote:

> Larry Knain wrote:
>
> > I should have said that this was a first attempt at using
> > Spirit and I was just experimenting
> > with some simple examples.
> >
> >  There are three examples in the code. The adjustment was
> > made to the second example which is for CSV.  The string to
> > be parsed was originally:
> >
> > char const *plist_csv = "\"string\",\"string with an embedded \\\"\","
> >         "12345,0.12345e4";
> > Changed to:
> >
> > char const *plist_csv = "\"string\",\"string with an embedded \\\"\","
> >         "12345,0.12345e4,,2";
> > These are at line 104.
>
> If you look at the parser definition, you'll notice, that this
> particular list parser is designed to parse escaped C-strings, integers
> or reals separated by commas. I.e. no empty elements. If you would like
> to make your list_p to match even empty elements, you'd have to make the
> list_csv_item optional:
>
>     list_csv =
>             list_p(
>                 !list_csv_item[append(vec_item)],
>     // ---------^ note this exclamation sign!
>                 ','
>             )[append(vec_list)]
>         ;
>
> > The original parser line was:
> >
> >  list_csv_item =
> >             confix_p('\"', *c_escape_ch_p, '\"')
> >         |   longest_d[real_p | int_p]
> >         ;
> > Again, I expected the null item to be omitted from my
> > experience with the tokenizer code but
> > I didn't expect the 2 to be omitted. After the initial
> > failure I changed the line to:
> >
> >  list_csv_item =
> >             confix_p('\"', *c_escape_ch_p, '\"')
> >         |   longest_d[real_p | int_p|~anychar_p]
> >         ;
> >
> > It made no difference. Inserting \"\" between the two commas
> > preceding the 2 did make it
> > get the "null" token and the 2.
>
> Adding the ~anything_p to the list_item parser isn't the correct thing.
> This actually won't match any input at all.
>
> HTH
> Regards Hartmut
>
>
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