Re: [Boost-users] [WAVE] position of tokens

9 Nov 2006


      Andreas Sæbjørnsen wrote:
...
Wow! You are fast! I have experimented a little bit with this 
code and it looks very good, but there are two things which 
needs to be fixed before I can use it:
    * the position of a token in the original source code is 
gone(default in standard Wave)
What do you mean by that?
...
* the line positioning is incorrect/non-standard (see 
below for an example).
This does not depend on the Wave library itself, but it's a matter of the
real_positions example. Do you mind to submit a fix for that (I now changed
the sample to output the detailed token information, which makes it easier
to track the output)?
...
The column information seems correct to me. But the line 
information is not correct as it does not behave like a 
standard preprocessor which would insert #line directives to 
map the positions to the original source file(s). Example:
///BEGIN TEST.C
#include "test.h"
#define FOO int x;
int main(){
FOO; /*comment */double y;
};
//END TEST.C
//BEGIN TEST.h
class Foo{
};
//END TEST.h
You would expect the line position of 'double' in test.C line 
5 to still be 5, but instead it is 6 because
   1. the line in test.C with just an "\n" in test.C does not 
count in the line positioning (-1 line in position)
   2. there is no separation between the lines in test.h and test.C
(+2 lines in position)
The real_positions example does not take into account #line directives, this
could be easily added, though. I simply didn't know, if you need it.

Regards Hartmut
...
thanks
Andreas
On 11/7/06, Hartmut Kaiser  wrote:
...
Andreas,
...
I need some advice regarding Wave. What I want to do is
...
...
with Wave on a token stream and extract the token stream 
representing macro calls after expansion. The twist is
...
...
the token stream after expansion to have the positions
to operate 
that I want 
that another
...
...
preprocessor would see on the already expanded output from Wave. 
E.g:
#define MACRO_CALL int x;
int main(){
     MACRO
};
Exands into
#line 2
int main(){
     int x;
};
Where 'int x' should have a position of line 3 instead of line 1 
after expansion. I also want the column number to 
represent what we 
see on line 3 instead of what we see on line 1. Is this possible ?
Ok, I've added a new pp hook (what else? :-P) to Wave:
//////////////////////////////////////////////////////////////////////
...
/////
//
//  The function 'generated_token' will be called by the library 
whenever a //  token is about to be returned from the library.
//
//  The parameter 'ctx' is a reference to the context 
object used for 
//  instantiating the preprocessing iterators by the user.
//
//  The parameter 't' is the token about to be returned 
from the library.
//  This function may alter the token, but in this case it 
must be //  
implemented with a corresponding signature:
//
//      Token const&
//      generated_token(Context const& ctx, Token& t);
//
//  which makes it possible to modify the token in place.
//
//  The default behavior is to return the token passed as the 
parameter //  without modification.
//
//////////////////////////////////////////////////////////////
/////////////
...
template 
    Token const&
    generated_token(Context const& ctx, Token const& t)
    { return t; }
This should help solving your problem.
To show how this hook function may help you I added a new sample 
'real_positions' to Wave demonstrating its use. Everything
is in the
...
Boost CVS::HEAD.
HTH
Regards Hartmut
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