Re: [Boost-users] [qi and lambda] Get wrong reaction of the qi::rule if I use lambda for the action

Subject: Re: [Boost-users] [qi and lambda] Get wrong reaction of the qi::rule if I use lambda for the action
From: boost_mailinglist_at_[hidden]
Date: 2011-08-16 05:41:30

Am 15.08.2011 16:21, schrieb TONGARI:
> 2011/8/15 TONGARI<tongari95_at_[hidden]>
>
>> 2011/8/15<boost_mailinglist_at_[hidden]>
>>
>> Hello,
>>>
>>> if I execute the following example, I get the following output "The bad
>>> one The good one a" but I only expected "The good one a".
>>>
>>> Why does it happens?  Boost 1.47.0 was used.
>>>
>>>
>>> #include<boost/config/warning_disable.**hpp>
>>> #include<boost/spirit/include/qi.hpp>
>>> #include<boost/lambda/lambda.hpp>
>>>
>>> #include<iostream>
>>>
>>> int main()
>>> {
>>>     using boost::spirit::qi::char_;
>>>     using boost::spirit::qi::parse;
>>>
>>>     char const *first = "{a}", *last = first + std::strlen(first);
>>>
>>>     parse(first, last, '{'>>  char_("a")[std::cout<<  "The good one "<<
>>> boost::lambda::_1<<  '\n'] |
>>>         char_("b")[std::cout<<  "The bad one "<<  boost::lambda::_1<<
>>> '\n']>>  '}');
>>>
>>>     return 0;
>>> }
>>>
>>
>> Because  (std::cout<<  "The good one ")&  (std::cout<<  "The bad one ") are
>> not lambda expressions so they are executed immediately, and it seems
>> Boost.Lambda just happened to work here.
>>
>> The corrected version would be:
>>
>> #include<boost/config/warning_disable.hpp>
>> #include<boost/spirit/include/qi.hpp>
>> #include<boost/spirit/include/phoenix.hpp>
>>
>>
>> #include<iostream>
>>
>> int main()
>> {
>>     using boost::spirit::qi::char_;
>>     using boost::spirit::qi::parse;
>>     using boost::spirit::qi::_1;
>>     using boost::phoenix::val;
>>
>>
>>     char const *first = "{a}", *last = first + std::strlen(first);
>>
>>     parse(first, last, '{'>>  char_("a")[std::cout<<  phx::val("The good one
>> ")<<  _1<<  '\n'] |
>>         char_("b")[std::cout<<  phx::val("The bad one ")<<  _1<<  '\n']>>
>> '}');
>>
>>     return 0;
>> }
>>
>
> Please omit phx:: before val.
>
>
>
>
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Thank you, it is working now.