David Abrahams:
Vesa Karvonen: > to the Boost Preprocessor library to help detect whether flag like > macros are defined. These macros would make it easier to move some > logic from unusable #if blocks into usable macros.
I got this idea while reading the following thread on the comp.programming newsgroup:Can you show an example of such a transformation?
http://groups.google.com/groups?dq=&hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=Xns92FA369D1BE1newspubwuggyorg%40217.32.252.50&prev=/groups%3Fq%3Dcomp.programming%26ie%3DUTF-8%26oe%3DUTF-8%26hl%3Den
I thought about suggesting use of macros (with help from Boost.Preprocessor), which would allow using code like this:
#pragma SECTION(RXFILTERS_C,rxdata,ADC_output)
// ...
While writing the answer, I got bored writing the "BOOL" versions of the macros, so I started thinking about how to detect whether a macro was defined. The BOOST_PP_IS_EMPTY(), etc... macros that I came up with are not a complete replacement for defined(), but they can help (especially in probably the most common case when a macro simply serves as a flag and is defined to be either empty or 1 (this excludes __cplusplus and many other compiler defined flags in the general case, btw)).
I think that repeating #if blocks, often using defined(), could be extracted from quite a few programs written in C or C++ that have been ported to multiple platforms. I don't have more specific examples in mind, however.
-Vesa Karvonen
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