5 ms·

Metaprogramming custom control structures in C

• comex 12y ago
  Some C hacks have advantages in theory but hard to use effectively, like named+default parameters via struct. Others are practical, but only if you don't care about compilers without GNU extensions (i.e. MSVC), such as RAII via attribute cleanup and safer macros via statement expressions. This control structure trick, despite being more esoteric looking than any of those, is both useful in practice and standard C. If you're defining a custom data container in C, it will let you write a foreach macro that doesn't require the user to declare any temporaries you need to use, doesn't break the break and continue statements, and doesn't require any weird syntax at the beginning of end of the loop. I highly recommend reading about it. For a (poorly documented) example of actual use from some code I wrote, see HTAB_FOREACH: https://github.com/comex/substitute/blob/master/lib/cbit/htab.h https://github.com/comex/substitute/blob/master/lib/cbit/hta... and the LET_LOOP macro it uses: https://github.com/comex/substitute/blob/master/lib/cbit/misc.h https://github.com/comex/substitute/blob/master/lib/cbit/mis...
  • nitrogen 12y ago
    I use named parameters in production C code for Nitrogen Logic. It just requires organizing things so that 0 is an acceptable default.
• pjlegato 12y ago
  Step 1: Write a Lisp interpreter in C. :)
  • dfox 12y ago
    Actually, probably most frequent users of really weird C preprocessor tricks are lisp implementations. (for the extreme example, CLISP has it's own custom C preprocessor)
  • davidw 12y ago
    Tcl actually has this ability, too, to write control structures in Tcl itself.
• deleted 12y ago
  [deleted]
• edward 12y ago
  Simon Tatham is the author of putty, he knows what he is talking about.
  • gosub 12y ago
    also author of my favourite puzzle collection http://www.chiark.greenend.org.uk/~sgtatham/puzzles/ http://www.chiark.greenend.org.uk/~sgtatham/puzzles/