Re: [Boost-users] Boost.Spirit's Greedy Fundamental Type Parsers

On Fri, 1 Apr 2016 09:07:30 +0200 Daniel Hofmann wrote:

On 04/01/2016 12:19 AM, Lee Clagett wrote:

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On Thu, 31 Mar 2016 23:02:05 +0200 Daniel Hofmann wrote:

...

Suppose I want to parse a list of ";"-separated floating point pairs with "," being the pair separator as in "1,2;3,4". Following this list comes a string literal representing a file extension, such as ".txt". [...] I am not sure why you want to use a `double` in this situation, but

std::vector<unsigned> out; parse(first, last, (+(uint_ >> '.') >> "txt"), out);

or

unsigned one = 0; boost::optional<unsigned> two; parse( first, last, (uint_ >> '.' >> -(uint_ >> '.') >> "txt"), one, two);

will prevent inputs that contain '-' or the various inputs that the real parser [1] accepts. uint_ [2] can also be specialized to have a min,max number of digits which might be useful to your situation.

I'm parsing into a std::vector<double> since I want both

1,2;3,4.txt

as well as

1.1,2.2;3.3,4.4.txt

to succeed. With a uint_ based parser as you suggest, I get a vector of {1,1,..} for the second example, which does not represent the input or lets me reconstruct it.

You could use the optional parser to store this information: +(uint_ >> '.' >> -(uint_ >> '.')) >> "txt" with attribute `vector>`.

Looking at strict_real_policies<double> I was under the impression that the default real policy should work for both inputs above, being able to parse both inputs into a vector of {1.0, 2.0, 3.0, 4.0} and {1.1, 2.2, 3.3, 4.4} respectively.

The `double_` parser will allow inputs like "+1.1.txt" or "1e1.txt". So hopefully these numbers are actual double values and not a versioning scheme. The `ureal_policies` trait can restrict valid inputs with some additional work. Overriding the behavior of `parse_exp`, `parse_exp_n`, `parse_nan`, and `parse_inf` to reject everything AND providing a static field `allow_leading_dot = false` might be enough. There is a grammar [0] on the real parsers page describing all the inputs allowed. Lee [0]http://www.boost.org/doc/libs/1_60_0/libs/spirit/doc/html/spirit/qi/referenc...