I wept when the author mentioned implementing SHA256 in macros.
Here is something similar: https://godbolt.org/z/Yj61b6GGj
I useed a non-cryptographic PRNG to write a C program that only compiles if you know the correct key.
Recursive macros in C, demystified (once the ugly crying stops)
41–50 of 90 posts
Re: Recursive macros in C, demystified (once the ugly crying stops)
#42Mildly related, sort of, one can prevent expansion of variadic macros as follows: #define printf(...) int (printf)(const char *, ...); I keep on seeing many random code bases just resort to #undef instead...
Doesn't this trigger warnings?
Re: Recursive macros in C, demystified (once the ugly crying stops)
#43Re: Recursive macros in C, demystified (once the ugly crying stops)
#44In many ways being limited ends up being a feature. Even limited as it is, you get some crimes against humanity like the bourne shell source, but at least most people agree it is a bad idea If it allowed more unlimited metaprogramming, building big complex things as macros might well have become popular
The CPP does allow quite advanced metaprogramming, it's just so obtuse to use and requires insane hacks so almost nobody does. See one of my favorite projects https://github.com/hirrolot/metalang99
Re: Recursive macros in C, demystified (once the ugly crying stops)
#45Mildly related, sort of, one can prevent expansion of variadic macros as follows: #define printf(...) int (printf)(const char *, ...); I keep on seeing many random code bases just resort to #undef instead...
Doesn't this trigger warnings?
Function like macros literally requires name( , i.e name followed directly by open paren, otherwise no macro substitution occurs.
so (name)() will always suppress function like macros (but not non-function ones, i.e regular #define name xxx)
Re: Recursive macros in C, demystified (once the ugly crying stops)
#46A C preprocessor implemented in Python:
https://github.com/paulross/cpip
Re: Recursive macros in C, demystified (once the ugly crying stops)
#47The behavior of C macros is actually described by a piece of pseudocode from Dave Prosser and it is not in the standard: * https://www.spinellis.gr/blog/20060626/ * https://www.spinellis.gr/pubs/jrnl/2006-DDJ-Finessing/html/S... * https://gcc.gnu.org/legacy-ml/gcc-prs/2001-q1/msg00495.html
Wow, I'm not sure I've ever seen this (or if I did, it was 20 years ago). And I was definitely looking around for this kind of history when I was searching around when writing. Perhaps my google skills have decayed... or google... or both! Thanks very much.
Oh, are you L33 T.?
Re: Recursive macros in C, demystified (once the ugly crying stops)
#48I think the C preprocessor was designed after the GPM clone m6, its successor m4, and Ratfor, so I suspect the difficulty in doing things like this is intentional. I guess I should ask McIlroy, who is responsible for pushing m4 to its absolute limits and was present when the C preprocessor was being designed: https://www.cs.dartmouth.edu/~doug/barem4.m4
_ Pure macros as a programming language
_
_ m4 is Turing complete even when stripped to the bare minimum
_ of one builtin: `define'. This is not news; Christopher
_ Strachey demonstrated it in his ancestral GPM, described in
_ "A general- purpose macrogenerator", The Computer Journal 8
_ (1965) 225-241.
_
_ This m4 program more fully illustrates universality by
_ building familiar programming capabilities: unlimited
_ precision integer arithmetic, boolean algebra, conditional
_ execution, case-switching, and some higher-level operators
_ from functional programming. In support of these normal
_ facilities, however, the program exploits some unusual
_ programming idioms:
_
_ 1. Case-switching via macro names constructed on the fly.
_ 2. Equality testing by redefining macros.
_ 3. Representing data structures by nested parenthesized lists.
_ 4. Using macros as associative memory.
_ 5. Inserting nested parameter symbols on the fly.
_
_ Idioms 2 and 5 are "reflective": the program writes code
_ for itself.
Re: Recursive macros in C, demystified (once the ugly crying stops)
#49The behavior of C macros is actually described by a piece of pseudocode from Dave Prosser and it is not in the standard: * https://www.spinellis.gr/blog/20060626/ * https://www.spinellis.gr/pubs/jrnl/2006-DDJ-Finessing/html/S... * https://gcc.gnu.org/legacy-ml/gcc-prs/2001-q1/msg00495.html
Thank you very much for providing these links!