Re: C++ / multiple instances / iostreams

[Hans Aberg]

At 14:15 +0200 2004/07/18, Laurence Finston wrote:
>> I've bison-1.875a installed and I've some questions to this version.
>>
>> 1) Does bison create an c++-parser class (wrapper) and can I use multiple
>> instances of the parser in an application?
>
>I've just been using 1.875, but the comments below might be helpful anyway.
>
>There's been some discussion about C++ parser classes recently,
>at least with respect to 1.875.
>You can look at the archives here:
>http://lists.gnu.org/archive/html/help-bison/
>
>I just generate a reentrant C parser and put C++ code in the actions for
>the rules.  It works fine.  I keep all the information about the parser
>state that I need in the object pointed to by the `void*' argument passed
>to `yyparse()'.  Therefore there's really no need for a parser class with
>`yyparse()' as a member function.  I use multiple threads that call
>`yyparse()' and that also works fine.

To this you must add that you are using %union and a Std-C++ compliant
compiler.  Then only POD's can be used in C++ unions, so they behave
essentially as under C, and as %union implements the parser semantic type
using a C union, it works. This does not work if one is using a semantic
type with non-POD data members, as the C stack will not invoke the copy
constructors when recopying.

Then, for that situation I made a C++ parser. The details are in the
Patches-Bison list. I need it, because, instead of a union type, I use a
polymorphic (virtual) class hierarchy. It does not work in a multi-threaded
environment; in order to achieve that, simply alter the skeleton file so
that the parser stack & other data are in the parser function.

>> 2) Does it support iostreams?
>
>If you use the method described above, this question becomes irrelevant,
>except with regard to the debugging output produced when using the `%debug'
>feature and `yydebug' is positive.

This is always irrelevat, except for diagnostic output, as the parser reads
tokens from the lexer, and not in any istream or other character flow.

  Hans Aberg