Let me elaborate a bit. Wave is built as a layered iterator. At the bottom
(on top of the iterators of the input stream) there is the lexer component
which constructs the C++ tokens from the input. The tokens you are looking
for (#ifdef etc.) are contained in the token sequence generated by the lexer
iterators.
On top of the lexer we have the preprocessing component which does the
actual preprocessing (as you might have expected). The token sequence
produced by the preprocessing component obviously doesn't contain these
tokens anymore.
What you could do in this situation is
- build your own lexer intercepting the tokens you're interested in and
storing the information you need somewhere else. This makes it very
difficult to track down the (virtual) position of these tokens in the
preprocessed token stream.
- adding some additional hooks to the library allowing to get notified on
these tokens. I'm not sure of the implications, though and how much this is
different from the first bullet :-P
- Perhaps you have another idea on this?
I was hoping to avoid modifying the lexer itself, so I have been more
reclined towards the approach of adding hooks to the library. I was
thinking more in the direction of
doing something similar to what struct
default_preprocessing_hooks (in preprocessing_hooks.hpp) does for
macros, since the user can reimplement this for the instantiation
of the template<> class context. Another option is to add this to
template<> class context much similar to the way it is currently
done for macros. What leads me to favour the struct
default_preprocessing_hooks solution over modifying template<>
class context is that it already handles similar problems and you
could also argue that these hooks does not fit in
template<> class context. So my two options are:
- add more hooks to struct default_preprocessing_hooks
- add more member functions which work as hooks within template<> class context
The hooks must be provided with all the necessary information for
extracting the preprocessor grammar and evaluating the preprocessor
conditionals. What do you think is the best solution,
its feasibility and how do you think it would fit into the wave preprocessor library?
> *evaluate the preprocessor conditionals
What do you have in mind? Do you mean the (macro-)expanded conditional
expression?
yes, so that I can extract the unexpanded preprocessor
conditional expression and when this expression is (macro-)expanded if
the result is positive or negative.
For instance in the example
#define BAR
#ifdef BAR
int x;
#ifdef FOO
int y;
#endif
#endif
I would be interested in extracting '#ifdef BAR' and also that it is
evaluated as true. I would also be interested in extracting '#ifdef
FOO' and that it is evaluated as false.
>
*after evaluating the preprocessor conditional,
> extract the portion which was evaluated as false as a string
>
> #define
positive
>
#ifdef int positive
> #endif /*Extract this false part as string*/ int x; #endif
Hmmm. This one is tough. The preprocessor is designed to skip this
information, so I'll have to look at the code base how to best access the
corresponding code fragments. Perhaps a special hook could be introduced to
get called for every skipped token.
That would be great! :) Do you think this can be done through struct default_preprocessing_hooks?
>
*I am also interested in the value and position
> of unexpanded macros
Undefined macros?
I am only interested in defined macros. To be more specific I am
interested in when the preprocessor recognises a macro. For each macro
it is interesting to extract the value and position in the file. The
macro can be found in two forms; the one before macro-expansion and the
one after. Both forms are interesting. But this is from what I have
seen already handled in struct default_preprocessing_hooks.
1: #define FOO int x;
2: FOO
On line 2 in this example code the macro FOO is found. This macro can
be expanded to 'int x', which to the preprocessor is equivalent to the
unexpanded macro FOO found on line 1.
>
*extracting the C/C++ statement or expression
> that the unexpanded macro (and expanded) is
> a part of.
This conceptually isn't possible at the preprocessor level because it has no
notion of a C++ statement/expression.
I do not want to use Wave as a C/C++ parser, only to understand a subst
of it's grammar. Let me corroborate for why I think it is doable and
that the information necessary to do this is already easily available.
What I was thinking was that
-since brackets ('{' and '}') and
semicolon should is found within the tokens from the lexer, you should
as far as I can see be able to fully define the grammar necessary to
recognize what can be an expression or statment. For instance a
variable declaration statement in C/C++ always ends with a ';'.
- a function definition statement has a basic
block (body) which is always limited by the bracket
({...}).
-reference expression also tend to end
with an ';', like for instance a function reference expression "
foo(); ".
Therefore I would argue that since I do not think that you need an
understanding of C/C++ syntax and only hopefully a fairly limited view
of the C/C++ grammar (and the information for this is in the
token-stream returned from the lexer) this should be doable. I think it
can be a little bit difficult though, but I have to draw on your
expertize here. Do you have any ideas for this?
>
*extract the value and position of all C and
> C++ comments
This one is easy. Just enable the preserve comments mode and all the comment
tokens will be part of the generated output token sequence.
Great. :) What about making a hook for this within stuct default_preprocessing_hooks also?
> Which work should I bace my work upon and which
> data structures should I reimplement and for what? I have
> looked at the documentation and the code, and it seems easy
> to do some parts but other are not obvious to me at this point.
Generally you should look at the existing preprocessing hooks and if these
can provide you with sufficient information. It should be quite straight
forward to add additional hooks to the library, so any suggestions are
welcome.