Re: [Boost-users] [wave] some more question...

From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2007-07-04 15:30:33

Hi Ovanes, 

> I have a file delived from some processor manufacturer which 
> I can not change. In the file I have following defines, which 
> wave can't parse:
> 
> #define UINT_MAX        4294967295U
> #define ULONG_MAX    1099511627775U
> 
> First error which happens during parsing of UINT_MAX is:
> 
> description: error: ill formed integer literal or integer 
> constant too large: 4294967295U
> 
> I do not understand why I get the first error, since the 
> value 4294967295U is 0xFFFFFFFF which is
> 32 bits long and should be fine (since it is also marked as 
> unsigned for the preprocessor)...

This was a bug in Wave which is fixed now. Thanks for reporting!

> Clearly the ULONG_MAX has a wrong numeric format (should be 
> 1099511627775UL or 1099511627775ul), but unfortunately this 
> file comes from some vendor and is deeply incorporated into 
> the build process, so that it can not easily be changed. What 
> do you think, could be the possible solution in this case?

Actually it should be 1099511627775ULL (at least on most 32 bit platforms),
and even then the preprocessor is not required to recognize it, since the
standard requires it to use long/unsigned long as the biggest internal
representation of integer literals.

To solve this I added the BOOST_WAVE_SUPPORT_LONGLONG_INTEGER_LITERALS
compile time configuration constant to Wave, which enables the usage of
boost::long_long_type/boost::ulong_long_type for the internal representation
of integer literals (only available on platforms supporting these types,
i.e. BOOST_HAS_LONG_LONG should be defined). 

If this is defined during compilaton of the library (not only your app!)
then Wave uses the long long types for all integer literals, even if the
suffix provided was only 'l' or 'ul' etc.

Note, that this option may slow down preprocessing a bit because long long's
may require some overhead if compared to long's.

Since the option breaks standards conformance it will be disabled by
default. But it's useful under certain circumstances (such as yours or when
you have to emulate other platforms).

The changes are committed to Boost::CVS head. Please note that in order to
implement this correctly I had to fix a bug in Spirit as well, which is
currently committed to the CVS::HEAD only (we'll try to get this into
1.34.1, but can't promise...).

> My other question would be:
> Is there any change to allow the hooking interface to 
> specify, which preprocessor directives should be expanded, an 
> which not. Let me summarize:
> 
> I need some few macros to be expanded, which are defined in 
> some 2-3 headers and I do not want wave to preprocess 
> everything (huge source dir). Ideally, it would be great to 
> have some functionality, which can notify the preprocessor 
> whether to skip the preprocessing directive or not, e.g. 
> function void found_include_directive(std::string const 
> &filename, bool include_next); (as well as other functions 
> like expanding_function_like_macro) from the 
> default_preprocessing_hooks interface could additionaly 
> return bool value, which would notify the preprocessor 
> whether to include and expand the file/macro or not. May be 
> in this second case I could solve the first problem as well, 
> since I don't really need these defines, they are parsed as 
> part of dependency, which is not required in my case.

This isn't implemented yet and requires a bit more effort to do so. Give me
some time to think about this, ok?

But there is another feature, which might be interesting for you in this
context. The Wave driver tool has some #pragma's allowing to redirect or
suppress the genereated output, which actually gives you some kind of
partial preprocessing feature:

#pragma wave option(output: "preprocessed/directory.hpp")

Where the argument to the output option may be a "file name", null (no
output), default (output as specified on the command line), or push/pop
(with the obvious semantics).

HTH
Regards Hartmut