What is the worst real-world macros pre-processor abuse you ve ever come across

Question

What is the worst real-world macros pre-processor abuse you ve ever come across  please no contrived IOCCC answers  haha     Please add a short snippet or story if it is really entertaining  The goal is to teach something instead of always telling people  never use macros      p s   I ve used macros before    but usually I get rid of them eventually when I have a  real  solution  even if the real solution is inlined so it becomes similar to a macro      Bonus  Give an example where the macro was really was better than a not-macro solution   Related question  When are C   macros beneficial

User · Answer

I like this example  it uses the macro to approximate the value of PI  The larger the circle  the more accurate the approximation    define   -F lt 00  --F-OO--  int F 00 OO 00 main   F OO   printf   1 3f n  4  -F OO OO   F OO                  - - -          - - - - - - - -       - - - - - - - - - - -     - - - - - - - - - - - - -    - - - - - - - - - - - - - -    - - - - - - - - - - - - - -   - - - - - - - - - - - - - - -   - - - - - - - - - - - - - - -   - - - - - - - - - - - - - - -   - - - - - - - - - - - - - - -    - - - - - - - - - - - - - -    - - - - - - - - - - - - - -     - - - - - - - - - - - - -       - - - - - - - - - - -           - - - - - - -               - - -        Another is the c program  c   To compile you need to define c as  -Dc   include  lt stdio h gt  int main     char  t    Hello World n    while  t  putc  t    stdout   return 0

User · Answer

I have used header files as big macros      compile-time-caller h  define param1      define param2      include  killer-header h      killer-header h    uses param1 and param2   I have also created recursive header files      compile-time-caller h  define param1      define param2      include  killer-header h      killer-header h   if        conditional taking param1 and param2 as parameters  define temp1 param1  define temp2 param2  define param1        expression taking temp1 and temp2 as parameters  define param2        expression taking temp1 and temp2 as parameters  include  killer-header h     some actual code  else    more actual code  endif

User · Answer

I did the following myself  and I think I learned something from it   In 1992 or so I wrote a small Lisp interpreter  It wasn t implemented in normal C  but in an interpreted C-like language  This C-like language used the standard C pre-processor  though   The Lisp interpreter of course contained the functions car  which is used in Lisp to return the first element in a list  and cdr  which returns the rest of the list  They were implemented like this   LISPID car LISPID id        CHECK CONS  car   1  id       return cons cars id - CONS OFFSET        car     LISPID cdr LISPID id        CHECK CONS  cdr   1  id       return cons cdrs id - CONS OFFSET        cdr       Data were stored in arrays  since there were no structs  CONS OFFSET is the constant 1000    car and cdr are used frequently in Lisp  and are short  and since function calls weren t very fast in the implementation language  I optimized my code by implementing those two Lisp functions as macros    define car id   CHECK CONS  car   1   id    cons cars  id  - CONS OFFSET    define cdr id   CHECK CONS  car   1   id    cons cdrs  id  - CONS OFFSET     CHECK CONS checks that its argument actually is a list  and since that one is also used frequently in the interpreter  and is short  I wrote that one too as a macro    define CHECK CONS fun  pos  arg            IS CONS arg                     LISP ERROR  Arg     pos     to     fun                             must be a list      lispid2string arg     0    IS CONS and LISP ERROR were also used frequently  so I made them into macros too    define IS CONS id            intp id   amp  amp   id   gt   CONS OFFSET             amp  amp    id  - CONS OFFSET   lt  sizeof cons cars     define LISP ERROR str       throw  str      n      Seems reasonable   But then  why did the entire system crash on this line   id2   car car car car  id1        I worked a long time to find the problem  until I finally checked what that short line was expanded to by the pre-processor  It was expanded to a 31370-character line  which I have here split into lines  502 of them  for clarity   id2       intp       intp       intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000      amp  amp         intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000      gt   1000  amp  amp          intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000          n      0   cons cars      intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000    - 1000      amp  amp         intp       intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000      amp  amp         intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000      gt   1000  amp  amp          intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000          n      0   cons cars      intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000    - 1000      gt   1000  amp  amp          intp       intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000      amp  amp         intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000      gt   1000  amp  amp          intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000          n      0   cons cars      intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000    - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp       intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000      amp  amp         intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000      gt   1000  amp  amp          intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000          n      0   cons cars      intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000          n      0   cons cars      intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000    - 1000    - 1000          n      0   cons cars      intp       intp       intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      amp  amp         intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000      gt   1000  amp  amp          intp   id1    amp  amp     id1    gt   1000  amp  amp      id1   - 1000   lt  sizeof cons cars      throw   Arg     1     to      car      must be a list      lispid2string   id1        n      0   cons cars  id1  - 1000     - 1000   lt  sizeof cons cars

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When I first came across macros in C they had me stumped for days  Below is what I was faced with  I imagine it makes perfect sense to C experts and is super efficient however for me to try and work out what exactly was going on meant cutting and pasting all the different macros together until the whole function could be viewed  Surely that s not good practice   What s wrong with using a plain old function     define AST LIST MOVE CURRENT newhead  field  do     typeof   newhead - gt first    list cur     new prev    AST LIST REMOVE CURRENT field     AST LIST INSERT TAIL  newhead     list cur  field       while  0

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I once put together this horrifying C   code which used macros to help hook functions into the import table of DLLs     define ARGLIST        VA ARGS     define CPPTYPELESSARG typelessParams  thisptr  typelessParams  define CPPTYPEDARG typedParams  void  thisptr  typedParams  define CPPTYPELESSNOARG thisptr  define CPPTYPEDNOARG void  thisptr   define CPPHOOKBODY hookName  params  void  thisptr          asm   mov thisptr  ecx         return On  hookName   params       define CHOOKBODY hookName  typelessParams  return On  hookName  typelessParams      define CPPHOOK InjectHookRef  importLib  importFunc  hookName  returnType  typedParams  typelessParams        HOOKIMPL InjectHookRef  importLib  importFunc  hookName  returnType  CPPTYPEDARG typedParams   typelessParams        typedParams    thiscall    stdcall  CPPHOOKBODY hookName  CPPTYPELESSARG typelessParams      define CPPHOOKNOARG InjectHookRef  importLib  importFunc  hookName  returnType  typedParams  typelessParams        HOOKIMPL InjectHookRef  importLib  importFunc  hookName  returnType  CPPTYPEDNOARG  typelessParams        typedParams    thiscall    stdcall  CPPHOOKBODY hookName  CPPTYPELESSNOARG     define CDECLHOOK InjectHookRef  importLib  importFunc  hookName  returnType  typedParams  typelessParams        HOOKIMPL InjectHookRef  importLib  importFunc  hookName  returnType  typedParams  typelessParams        typedParams    cdecl    cdecl  CHOOKBODY hookName  typelessParams     define CDECLFUNC name  address  returnType  args        typedef returnType    cdecl  name  Ptr  args         name  Ptr name    name  Ptr  address    define CPPFUNC name  address  returnType  args        typedef returnType    thiscall  name  Ptr  void  thisptr  args         name  Ptr name    name  Ptr  address    define STDFUNC name  address  returnType  args        typedef returnType    stdcall  name  Ptr  args         name  Ptr name    name  Ptr  address    define STDHOOK InjectHookRef  importLib  importFunc  hookName  returnType  typedParams  typelessParams        HOOKIMPL InjectHookRef  importLib  importFunc  hookName  returnType  typedParams  typelessParams        typedParams    stdcall    stdcall  CHOOKBODY hookName  ARGLIST typelessParams      define HOOKIMPL InjectHookRef  importLib  importFunc  hookName  returnType  typedParams  typelessParams  hookParams  fnPtrCall  hookCall  hookBody            typedef returnType  fnPtrCall    hookName  OrigPtr    typedParams              class hookName   public IHook                       public                typedef hookName  OrigPtr func type            private                static void  m origFunction                static bool m bModifyImport                static std  string m lib                static std  string m importFunc                static std  string m sHookName                static returnType hookCall hookName  FnHook   hookParams                                     hookBody                               static bool ImplIsModifyImport     return hookName  m bModifyImport                  static void ImplSetModifyImport bool bModify    hookName  m bModifyImport   bModify                  static const std  string  ImplGetLibName     return hookName  m lib                  static const std  string  ImplGetImportFunctionName     return hookName  m importFunc                  static void ImplSetOriginalAddress void  fn    hookName  m origFunction   fn                  static void  ImplGetOriginalAddress     return hookName  m origFunction                  static returnType On  hookName   typedParams                  static void  ImplGetNewAddress     return hookName    hookName  FnHook                  static const std  string  ImplGetHookName     return hookName  m sHookName              public                hookName                                     InjectHookRef AddHook  IHook  this                     hookName  m lib   importLib                    hookName  m importFunc   importFunc                    hookName  m sHookName    hookName                    hookName  m origFunction   NULL                    hookName  m bModifyImport   true                                virtual bool IsModifyImport   const   return hookName  ImplIsModifyImport                    virtual void SetModifyImport bool bModify    hookName  ImplSetModifyImport bModify                   virtual const std  string  GetHookName   const   return hookName  ImplGetHookName                    virtual const std  string  GetLibName   const   return hookName  ImplGetLibName                    virtual const std  string  GetImportFunctionName   const   return hookName  ImplGetImportFunctionName                    virtual void  GetOriginalAddress   const   return hookName  ImplGetOriginalAddress                    virtual void  GetNewAddress   const   return hookName  ImplGetNewAddress                    virtual void SetOriginalAddress void  fn    hookName  m origFunction   fn                  static func type GetTypedOriginalAddress     return reinterpret cast hookName  m origFunction                            void  hookName  m origFunction   NULL            bool hookName  m bModifyImport   false            std  string hookName  m lib            std  string hookName  m importFunc            std  string hookName  m sHookName            static hookName g  hookName  Inst    Which in turn allowed me to do this    CPPHOOK gIH   SimEngine dll     AddEntity Player  UAEXPAVEntity   Z   PlayerAddEntity  void  void  ent  ent       Called when the engine calls Player  AddEntity entity     void PlayerAddEntity  OnPlayerAddEntity void  thisptr  void  ent        unsigned int id   getPlayerID thisptr    gIH GetLog  - gt Info  Player  d adding entity  s         getPlayerID thisptr   getEntityName ent     gPlayers id    thisptr     if  id    2  amp  amp  gPlayers 1   amp  amp  gPlayers 2        EntitySetOwner  GetTypedOriginalAddress    ent  gPlayers 1        gEnts ent    Entity ent  Vector3f      PlayerAddEntity  GetTypedOriginalAddress    thisptr  ent

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This is taken from a popular open source program  In fact it makes some parts of the code more readable by hiding the ugly legacy    define EP STATUS    CASTLING   BOARD FILES-2   define HOLDINGS SET CASTLING   BOARD FILES-1    I guess there is nothing really bad here  I just find it funny   http   git savannah gnu org cgit xboard git tree common h

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A past employer found there were no implementations of BASIC-PLUS on modern Unix systems  so they tried to re-implement it using C pre-processor macros    define IF if   define THEN      define ENDIF    define GOTO goto L      etc     Horrific

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A  technical manager  who had formerly been a coder introduced the following wonderful macros into our C   project because he thought that checking for NULL values in DOM parsing routines was just too much work   TRYSEGV CATCHSEGV   Under the covers  these used setjmp  longjmp  and a signal handler for SIGSEGV to emulate the ability to  catch  a segfault   Of course  nothing in the code reset the jump pointed once the code had exited the scope of the original TRYSEGV macro invocation  so any segfault in the code would return to the  now invalid  jump env pointer   The code would immediately die there  but not before destroying the program stack and rendering debugging more or less pointless

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Anything using sendmail and its magic configuration syntax

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define unless cond  if  cond   define until cond  while  cond    Used   unless  ptr    NULL       ptr- gt foo

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define FLASE FALSE   The programmer was a bad typist  and this was his most common mistake

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define protected private   Seemed like a good idea sometimes  but if you need to  you should probably just string replace anyway   Protected is fairly evil  allowing internal access to descendants isn t much better than just making the items public

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The obligatory   define FOR  for   and   define ONE  1  define TWO  2       Who knew

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Good macros   although personally I dislike the double parentheses required to use this syntax  I prefer either vararg macros  C99 only  or something like PRINTF 0  PRINTF 1  etc  depending on the number of arguments    ifdef DEBUG  define PRINTF x  printf x  else  define PRINTF x   endif   Reduces code size   execution time  the first more than the second  for non-debug build  also prevents leaking debug text strings which may pose a smallish security risk

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I once had to port a C application from unix to windows  the specific nature of which shall remain unnamed to protect the guilty   The guy who wrote it was a professor unaccustomed to writing production code  and had clearly come to C from some other language   It also happens that English wasn t his first language  though the country he came from the majority of people speak it quite well   His application made heavy use of the preprocessor to twist the C language into a format he could better understand   But the macros he used the most were defined in a header file named  Thing h   seriously   which included the following    define I  Any void me  define thou  Any void thee  define iam klas   klas me    klas  void me  define thouart klas   klas thee    klas  void thee  define my  me - gt   define thy  thee - gt   define his  him - gt   define our  my methods - gt   define your  thy methods - gt       which he then used to write monstrosities like the following   void Thing setName  I  const char  name    iam  Thing   if  name    my name        Melder free  my name       my name   Melder wcsdup  name             our nameChanged  me      void Thing overrideClass  I  void  klas    iam  Thing   my methods    Thing Table klas  if      Thing Table  klas  - gt  destroy        Thing Table  klas  - gt   initialize  klas       The entire project   60 000 LOC  was written in a similar style -- marco hell  weird names  Olde-English jargon  etc   Fortunately we were able to throw the code out since I found an OSS library which performed the same algorithm dozens of times faster    I ve copied and edited this answer which I originally made on this question

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The use of the LINE preprocessor to generate unique ID for messages passed over the network   NetworkMessages h   define MSG LOGIN    LINE    define MSG LOGOUT   LINE    define MSG CHAT     LINE     This is an example where the macro really was better than a non-macro solution   In a non-macro solution classes  functions and variables have to be built to keep track of what ID the message is  The developer may or may not make the message ID tracking complicated whereas this is easier to read and debug   In addition  its easier to add new messages just by adding the message into the source   The disadvantage of this situation is that the file has to be included in all code that uses messages  Compile time would increase whenever a message is edited

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A mix between Pascal syntax and french keywords    define debut    define fin    define si if   define alors     define sinon  else   define finsi

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define interface struct   in some of Optima   headers  Optima   is was a Watcom Powersoft IDE I had to work with

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I m adding another one that has started to annoy me over time    define ARRAYSIZE x   sizeof x  sizeof  x  0      And that s if they get it right  I ve seen versions with all possible permutations of parenthesis present or not   I ve seen it defined twice in the same header file   Mainly my argument applies to Windows  though I assume other OS SDKs have something similar   where just about everyone seems to feel the need to define this macro in their project s header  and I don t understand why     WinNT h  which is included by Windows h  defines a very nice version that does some template voodoo to cause compile time errors if you pass a pointer type instead of an array     Of course it falls back to exactly what I wrote above if you are building a C program  but I would still not redefine something the SDK has by default for no reason

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Coroutines  AKA Stackless threads  in C       It s Evil trickery    define crBegin static int state 0  switch state    case 0   define crReturn i x  do   state i  return x  case i     while  0   define crFinish   int function void        static int i      crBegin      for  i   0  i  lt  10  i            crReturn 1  i       crFinish     int decompressor void        static int c  len      crBegin      while  1            c   getchar            if  c    EOF              break          if  c    0xFF                len   getchar                c   getchar                while  len--              crReturn c             else         crReturn c             crReturn EOF       crFinish      void parser int c        crBegin      while  1               first char already in c            if  c    EOF              break          if  isalpha c                 do                   add to token c           crReturn                   while  isalpha c                got token WORD                     add to token c           got token PUNCT       crReturn               crFinish

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define PROCESS AND RETURN X    X process         Important  Return only after invoking virtual method process     return X   Due to  Important  comment  the macro never returns the object and CRASH

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define  CR LF    r    That confused the hell out of me for a while

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The NFS code in BSD-kernels use goto between macros  It s still in use  and the code actually works  I know of several persons who have tried to clean it up  but all of them have given up after a while - it s just too messy   You can see it here  http   www openbsd org cgi-bin cvsweb src sys nfs nfsm subs h rev 1 43

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Windows h has a lot of functions that abused macros     MrValdez is annoyed by the GetObject macro found in Windows h  The GetObject macro changes the GetObject   function into GetObjectA   or GetObjectW    depending if the build is compiled in non-unicode and unicode  respectively   MrValdez hates having to do before the GetObject function line   undef GetObject  Object  GetObject     The alternative is to change the function name to something else like GetGameObject      jdkoftinoff in the comments have nailed it  The problem is that all windows API functions are macros   Adam Rosenfield mentioned that that the issues can be fixed by defining NOGDI  WIN32 LEAN AND MEAN  NOMINMAX  etc before including windows h to remove the issues

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I was bored one day and was playing around with blocks in Objective-C      define Lambda var  body     id id  var     return  body    copy   define Call f  arg    id    id   f   arg   define Int num   NSNumber numberWithInteger  num    define Mult a  b  Int   a  integerValue      b  integerValue    define Add a  b  Int   a  integerValue      b  integerValue    define Sub1 n  Int   n  integerValue  - 1   define Add1 n  Int   n  integerValue    1   define If cond  thenblock  elseblock     cond  integerValue     thenblock     elseblock    define Cons car  cdr     ConsType alloc  initWithCar  car  cdr  cdr     define Car list    list  car   define Cdr list    list  cdr   define Define var  value  id var    value   define Nullq value  Int value    nil    allowing  interesting  things like   Define Y  Lambda f  Call Lambda x  Call x  x                             Lambda x  Call f  Lambda y  Call Call x  x   y         Define AlmostTotal  Lambda f  Lambda list  If Nullq list   Int 0                                                 Add Car list   Call f  Cdr list         Define Total  Call Y  AlmostTotal    Print Call Total  Cons Int 4   Cons Int 5   Cons Int 8   nil          some function and class definitions not shown for sake of brevity

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My worst    define InterlockedIncrement x   x     define InterlockedDecrement x   x --   I spent two days of my life tracking down some multi-threaded COM ref-counting issue because some idiot put this in a header file   I won t mention the company I worked for at the time     The moral of this story   If you don t understand something  read the documentation and learn about it   Don t just make it go away

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See this answer re how a dyslexic colleague made life easier for themselves with a common header file full of things like  define fasle false

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I m not fond of the Boost Preprocessor stuff  I attempted once to figure out how to use it  we had Boost in the project anyway      but as near as I could tell  using it would make my error messages SO unreadable that it wasn t worth it   I liked the idea of the equivalent of looping macros  but it was just too much

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At Lucent  I once took a look at the source code of Steve Bourne s original Unix shell  and  found he d used the C pre-processor to make C look like Pascal or Algol   The part dealing with if statements looked like this    define IF   if    define THEN      define ELSE   else    define ELIF   else if    define FI         A friend of mine told me he d done some maintenance on it in the mid-1990s  and it was still the same    There s a lesson here for us in the inherent conservatism of a code base    Of course Steve did this as an experiment in the early days  and I m sure would have had second thoughts if he d written it later    Update  According to Wikipedia s Bourne Shell article  the macros gave it an Algol 68 flavor   And  the full set of macros is here   They apparently influenced the founders of the International Obfuscated C Code Contest

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I would like to submit for the contest a gem called chaos-pp  which implements a functional language by means of the preprocessor macros   One of the examples is calculating the 500th fibonacci number entirely by the preprocessor   The original code before preprocessor looks as this   int main void       printf        The 500th Fibonacci number is         ORDER PP 8stringize 8to lit 8fib 8nat 5 0 0               n       return 0      preprocessing the file we get the following result  after a rather long wait      cpp -I   inc fibonacci c 2 gt  dev null   tail   return fib iter n  0  1       63  fibonacci c  int main void       printf        The 500th Fibonacci number is          139423224561697880139724382870407283950070256587697307264108962948325571622863290691557658876222521294125           n       return 0

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An  architect   very humble guy  you know the type  had the following    define retrun return   because he liked to type fast  The brain-surgeon used to like to shout at people who were smarter than him  which was pretty much everyone   and threaten to use his black-belt on them

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From memory  it looked something like this    define RETURN result  return  result     int myfunction1 args        int x   0         do something     RETURN x   int myfunction2 args        int y   0         do something     RETURN y   int myfunction3 args        int z   0         do something     RETURN z    Yes that s right  no closing braces in any of the functions   Syntax highlighting was a mess  so he used vi to edit  not vim  it has syntax coloring    He was a Russian programmer who had mostly worked in assembly language   He was fanatical about saving as many bytes as possible because he had previously worked on systems with very limited memory    It was for satellite   Only very few byte  so we use each byte over for many things     bit fiddling  reusing machine instruction bytes for their numeric values   When I tried to find out what kinds of satellites  I was only able to get  Orbiting satellite   For making to orbit    He had two other quirks  A convex mirror mounted above his monitor  For knowing who is watching   and an occasional sudden exit from his chair to do a quick ten pushups   He explained this last one as  Compiler found error in code  This is punishment

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define if while   It was joke played on someone  it wasn t found amusing by those affected

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The worst abuses  and I m guilty of doing this occasionally  is using the preprocessor as some sort of data file replacement  ie    define FOO RELATION     BAR TUPLE  A  B  C      BAR TUPLE  X  Y  Z       and then somewhere else    define BAR TUPLE  p1  p2  p3  if  p1   p2   p3  FOO RELATION  undef BAR TUPLE   which will result in   if  A   B   C  if  X   Y   Z    This pattern can be used to do all sorts of  terrible  stuff    generate switch statements or huge if else blocks  or interface with  real  code  You could even use it to   cough   generate a context menu in a non-oo context menu system   cough    Not that I d ever do anything so lame   Edit  fixed mismatched parenthesis and expanded example

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define ever      for ever

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Directly from Qt    define slots          define signals         Really nice to interact with other libs as boost  signals    Just an example  there are many others in Qt that create funny looking code like   class X   public QObject      Q OBJECT private slots           public signals                And that is C      but suddenly   boost  signals  trackable   Is not valid C   any more

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I agree that for the most part  macros are horrible to use  but i have found a few instances where they have been useful   This one is actually brilliant IMHO  as you can only get something similar with sprintf  which then requires resource allocations and whatnot  plus  all work is done entirely by the preprocessor     Macro  Stringize            Converts the parameter into a string     define Stringize  L             L      Macro  MakeString            Converts the contents of a macro into a string     define MakeString  L       Stringize L       Macro   LINE            Gets the line number as a string     define  LINE                   MakeString    LINE          Macro   FILE POS            Gets the current file name and current line number in a format the Visual Studio         can interpret and output goto       NOTE  For VS to properly interpret this  it must be at the start of the line  can only have whitespace before      define  FILE POS                 FILE        LINE          The other that I loathe to use  but find it extremely useful is doing something like this  which basically allows me to quickly generate templates that have a variable number of template parameters   define TEMPLATE DEFS    typename ReturnType  define TEMPLATE DECL   ReturnType  define FUNCTION PARAMS void  define FUNCTION PASS     define GENERIC CALLBACK DECL NAME      CallbackSafePointer0  include  Callback inl    define TEMPLATE DEFS   typename ReturnType  typename P1  define TEMPLATE DECL   ReturnType  P1  define FUNCTION PARAMS P1 param1  define FUNCTION PASS   param1  define GENERIC CALLBACK DECL NAME      CallbackSafePointer1  include  Callback inl    define TEMPLATE DEFS   typename ReturnType  typename P1  typename P2  define TEMPLATE DECL   ReturnType  P1  P2  define FUNCTION PARAMS P1 param1  P2 param2  define FUNCTION PASS   param1  param2  define GENERIC CALLBACK DECL NAME      CallbackSafePointer2  include  Callback inl    define TEMPLATE DEFS   typename ReturnType  typename P1  typename P2  typename P3  define TEMPLATE DECL   ReturnType  P1  P2  P3  define FUNCTION PARAMS P1 param1  P2 param2  P3 param3  define FUNCTION PASS   param1  param2  param3  define GENERIC CALLBACK DECL NAME      CallbackSafePointer3  include  Callback inl      and so on      Although this makes it kind of horrible to read  Callback inl   it does completely eliminate rewriting the same code with a different number of arguments  I should also mention that  Callback inl   undefs all of the macros at the end of the file  hence  the macros themselves won t interfere with any other code  it just makes  Callback inl  a little harder to write  reading and debuging isn t too hard though

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Another piece of  creative  use of the preprocessor  though it is more in the terminology employed than in the mechanics  which are incredibly mundane                                                                                OS2 and PCDOS share a lot of common codes   However  sometimes    OS2 needs codes similar to those of UNIX   NOTPCDOS is used in these    situations       ifdef OS2  define PCDOS  define NOTPCDOS  else    OS2     ifndef PCDOS  define NOTPCDOS  endif    PCDOS     endif    OS2      Genuine code - I thought I d removed it  but apparently not   I must have done so out in some temporary branch and not gotten permission to check it back into the main code   One more item for the  to do  list

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I maintain code that has gotos in macros  So a function will have a label at the end but no visible goto in the function code  To make matters worse the macro is at the end of other statements usually off the screen unless you scroll horizontally    define CHECK ERROR if   SomeCondition  goto Cleanup  void SomeFunction           SomeLongFunctionName ParamOne  ParamTwo  ParamThree  ParamFour   CHECK ERROR         SomeOtherCode       Cleanup           Cleanup code

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The hideous    define begin    define end      and so on      Seriously  if you want to code in Pascal  buy a Pascal compiler  don t destroy the beautiful C language

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ASA - http   www ingber com  ASA  You really have to download it to appreciate it  The entire work flow is determined by macros  It is completely unreadable  As an example -    if  asa open    FALSE    asa open   TRUE    number asa open   if ASA PRINT if  number asa open    1         open the output file     if USER ASA OUT   if   strcmp  OPTIONS- gt Asa Out File   STDOUT       if INCL STDOUT     ptr asa out   stdout   endif    INCL STDOUT        else    if ASA SAVE     ptr asa out   fopen  OPTIONS- gt Asa Out File   a     else     ptr asa out   fopen  OPTIONS- gt Asa Out File   w     endif      else    USER ASA OUT      if   strcmp  ASA OUT   STDOUT       if INCL STDOUT     ptr asa out   stdout   endif    INCL STDOUT        else    if ASA SAVE     ptr asa out   fopen  ASA OUT   a     else     ptr asa out   fopen  ASA OUT   w     endif      endif    USER ASA OUT      else    if USER ASA OUT   if   strcmp  OPTIONS- gt Asa Out File   STDOUT       if INCL STDOUT     ptr asa out   stdout   endif    INCL STDOUT        else       ptr asa out   fopen  OPTIONS- gt Asa Out File   a         else   if   strcmp  ASA OUT   STDOUT       if INCL STDOUT     ptr asa out   stdout   endif    INCL STDOUT        else       ptr asa out   fopen  ASA OUT   a         endif   fprintf  ptr asa out    n n t t number asa open    d n              number asa open      endif    ASA PRINT      else     recursive asa open   if ASA PRINT if  recursive asa open    1         open the output file     if ASA SAVE  if USER ASA OUT   if   strcmp  OPTIONS- gt Asa Out File   STDOUT       if INCL STDOUT     ptr asa out   stdout   endif    INCL STDOUT        else       ptr asa out   fopen  OPTIONS- gt Asa Out File   a         else   if   strcmp  ASA OUT   STDOUT       if INCL STDOUT     ptr asa out   stdout   endif    INCL STDOUT        else       ptr asa out   fopen  ASA OUT   a         endif  else    ASA SAVE     if USER ASA OUT   if   strcmp  OPTIONS- gt Asa Out File   STDOUT       if INCL STDOUT     ptr asa out   stdout   endif    INCL STDOUT        else     etc   etc   And that is just setting up the options  the entire program is like that

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I found it in libtidy        Internal symbols are prefixed to avoid clashes with other libraries      define TYDYAPPEND str1 str2  str1  str2   define TY  str  TYDYAPPEND prvTidy str    TY  DocParseStream  bar foo     The problem is that visual studio 2005 and maybe other ide go to definition and go to declaration features only find the  define TY       and not the desired DocParseStream declaration   Maybe it is safer this way   I think they should put a prefix for each function and not call a macro to do the job   it s cluttering the code   but maybe I am wrong about that  What do you think     Ps  It seems that almost all the internal function const and others are prefixed using this   My colleague just told me that it is usual   wtf  Maybe I missed something

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include  lt iostream gt   define System S s s  define public  define static  define void int  define main x  main   struct F void println char  s  std  cout  lt  lt  s  lt  lt  std  endl     struct S F out     public static void main String   args      System out println  Hello World         Challenge  Can anyone do it with fewer defines and structs   -

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Anything that uses the Token concatenation operator      I ve seen this used to hack together psudo-template systems in C   and other horrible things  The worst thing about using it is how impossibly cryptic your error messages become   I have seen one good use for it however  There was a macro      MONITOR COMPONENT classname   that generated classes at compile time that would inherit from a predefined monitor class and classname and that would autoregister with a singleton class that was used to monitor each component   Did it work  Yes  was it the nicest way of doing it   probably not

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Have to do this from memory  but was about like this  Working with a lib for writing Symbian apps  Hidden in a header file you needed to include was this little gem      Here come the register defines   define C  lt something gt   define N  lt something gt   lt two more single letter defines gt    In our code the loading of a file with a hardcoded filename failed  When we changed the file location from C to D drive  it magically worked

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In one year of the International Obfuscated C Coding Contest  there was an entry where the entire program was   P  With the proviso that you could define P in the makefile to be whatever program you wanted   As I recall  it won in one of the categories  and the next year a rule had popped up disallowing that style of entry    Edit  six months later or something    I m sure the  No IOCCC  thing wasn t in the main question when I wrote this

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The worst one I saw was the non-use  -   Someone wrote a strcpy  I think that was it    over 10 years ago now  function inside of a method  because they didn t want the overhead of calling strcpy    sigh    They clued in that it wouldn t work for Japanese characters so they added an  if  at the start to do ASCII or Unicode   At that point the code was about a screen long    likely killing cache coherency and erasing his supposed savings for the inlining of the code   The code was identical save for the types  so should have used a macro    Of course the strcpy that they wrote was much much much slower than the hand tuned assembler one that was in the standard library     Of course if they had just done it all as a macro it could have been replaced with a call to strcpy     Of course I quit the company  not directly because of that

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The worst I ve ever encountered was in a product containing a suite of executables where the designated technical leader hadn t figured out libraries   Instead  he had sets of files that were shared in several Visual Source Safe folders  He then realised they needed to behave slightly differently for each application    There s a number of refactoring steps you could apply here   Instead  he used  ifdefs     void DisplayLoadError            if defined   TIMETABLE EDITOR    MessageBox  Timetable Editor failed to load the correct timetable   MB ERROR       else if defined   SCHEDULESET EDITOR    MessageBox  Schedule Set Editor faied to load the correct Schedule Set   MB ERROR       else if defined   ROSTER EDITOR    MessageBox  Roster Editor failed to load the correct Roster   MB ERROR       endif

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switch  device id     ifndef PROD 1  ifndef PROD 2  ifdef PROD 3   case ID 1   endif   ifdef PROD 4   ifdef PROD 5   case ID 2    case ID 3    case ID 4   elif defined PROD 4   ifndef PROD 6   case ID 1   endif    PROD 6   case ID 5   endif    case ID 6   endif   ifdef PROD 7    ifndef PROD 8     case ID 7     endif  endif    names changed to protect the not so innocent   Notice that we haven t even gotten to any code yet  this is just to get to the first actual bit of code   This actually happens  in almost  but not exactly the same way  for several functions  each of which  in the end only have 4 possible variations  which are also mostly copy paste with slight variations and  ifdefs of their own

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It s not a C macro but     Many years ago I had the fun task of porting the original Transport Tycoon from the PC to the Mac  The PC version was written entirely in assembler so we had to go through the whole source code and port it to  PC  C code first and then port that to the Mac  Most of the code was OK  even object orientated in places  However  the world rendering system was unbelievable  For anyone who s not played the game  the world can be viewed at one of three zoom levels  The code for this was something along the lines of   macro DrawMacro  lt list of arguments gt     a couple of thousand lines of assembler with loads of conditionals    based on the macro arguments  DrawZoomLevel1     DrawMacro  lt list of magic numbers gt   DrawZoomLevel2     DrawMacro  lt list of more magic numbers gt   DrawZoomLevel3     DrawMacro  lt list of even more magic numbers gt    We must have been using a slightly older version of MASM as the macro would crash the assembler when we tried to assemble it   Skizz

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Try to debug big project that really loves macros   and there is a lot of macros that calls other macros that calls other macros etc etc    5-10 levels of macros was not that uncommon   And then top it up with a lot of  ifdef this macrot  else that macro   so if you follow the code it like a tree of different paths it can go   The only solution is most cases was to precompile and read that instead

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A coworker and I found these two gems in some of our code for object streaming   These macros were instantiated in EVERY SINGLE class file that did streaming   Not only is this hideous code spewed all over our code base  when we approached the original author about it  he wrote a 7 page article on our internal wiki defending this as the only possible way to accomplish what he was attempting to do here    Needless to say  it has since been refactored out and is no longer used in our code base   Don t be thrown off by the highlighted keywords   This is ALL a macro   define DECLARE MODIFICATION REQUEST PACKET  T                                                    namespace NameSpace                                                                                                                                                                                                                                                           class T  ElementModificationRequestPacket                                                                                                                                                                                                                                                 DECLARE STREAMING TEMPLATES  IMPEXP COMMON TEMPLATE DECLARE  NameSpace  ElementModificationRequestPacket lt T gt   OtherNameSpace  NetPacketBase        DLLIMPEXP COMMON TEMPLATE DECLARE  NameSpace  ElementModificationRequestPacket lt T gt          DECLARE AUTOGENERATION TEMPLATES  DLLIMPEXP COMMON TEMPLATE DECLARE  NameSpace  T  ModificationRequestPacket  NameSpace  ElementModificationRequestPacket lt T gt                                                                                                     namespace NameSpace                                                                       class DLLIMPEXP COMMON T  ModificationRequestPacket   public ElementModificationRequestPacket lt T gt                                                                                             public                                                                                        T  ModificationRequestPacket  NetBase   pParent                                             ElementModificationRequestPacket lt T gt   pParent    m Gen                                                                                                                                 T  ModificationRequestPacket  NetBase   pParent                                                                   Action          eAction                                                                   const T  amp    rT                                                      ElementModificationRequestPacket lt T gt   pParent  eAction  rT    m Gen                                                                                                                    T  ModificationRequestPacket  const T  ModificationRequestPacket  amp  rhs                                  ElementModificationRequestPacket lt T gt   rhs    m Gen                                                                                                                                     virtual                      T  ModificationRequestPacket  void                                                                                                                             virtual Uint32          GetPacketTypeID  void   const                                                                                                                               return Net  T   Modification REQUEST PACKET                                                                                                                                                                                                                                   virtual OtherNameSpace  ClassID GetClassID   void   const                                                                                                                               return OtherNameSpace  NetBase  GenerateHeader  OtherNameSpace  ID  LICENSING                                                              Net  T   Modification REQUEST PACKET                                                                                                                                                                                                 virtual T  ModificationRequestPacket   Create  void   const                                     return new T  ModificationRequestPacket  m pParent                                                                                                                                        T  ModificationRequestPacket                                                                                                                                                            protected                                                                                     OtherNameSpace  ObjectAutogeneration lt T  ModificationRequestPacket gt  m Gen                                                                                                                        friend class OtherNameSpace  StreamingBase  StreamingClassInfoT lt T  ModificationRequestPacket  gt                             OtherNameSpace  StreamingBase  Streaming lt T  ModificationRequestPacket  ElementModificationRequestPacket lt T gt   gt     m Stream                                                                                                                                                                                                                                                                                    DLLIMPEXP COMMON TEMPLATE DECLARE  ThirdNameSpace  ListenerBase lt const NameSpace  T  ModificationRequestPacket gt                 DLLIMPEXP COMMON TEMPLATE DECLARE  ThirdNameSpace  BroadcasterT lt const NameSpace  T  ModificationRequestPacket gt                 typedef  ThirdNameSpace  BroadcasterT lt const T  ModificationRequestPacket gt   T  ModifiedBroadcaster      define IMPLEMENT MODIFICATION REQUEST PACKET  T                                                                      DLLIMPEXP COMMON TEMPLATE INSTANTIATE  NameSpace  ElementModificationRequestPacket lt T gt                              DLLIMPEXP COMMON TEMPLATE INSTANTIATE  ThirdNameSpace  ListenerBase lt const NameSpace  T  ModificationRequestPacket gt             DLLIMPEXP COMMON TEMPLATE INSTANTIATE  ThirdNameSpace  BroadcasterT lt const NameSpace  T  ModificationRequestPacket gt             INSTANTIATE STREAMING TEMPLATES  DLLIMPEXP COMMON TEMPLATE INSTANTIATE  NameSpace  ElementModificationRequestPacket lt T gt   OtherNameSpace  NetPacketBase     INSTANTIATE AUTOGENERATION TEMPLATES  DLLIMPEXP COMMON TEMPLATE INSTANTIATE  NameSpace  T  ModificationRequestPacket  NameSpace  ElementModificationRequestPacket lt T gt        Update  December 17  2009    More good news regarding this hideous macro author   As of August  the employee responsible for this monstrosity was sacked

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By a classmate who failed to understand the rules about magic numbers   define TWO HUNDRED AND EIGHTY THREE POINT ONE 283 1

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The worst I ve seen is in my current project where there are a whole lot of cases of    if PROGRAMA                   if                                  else                  if                                  endif          Yeah  he closes 2 opens with a single close

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AI Game Programming Wisdom has a chapter where macros were used to create a scripting language for finite state machines    Since the book and code are copyrighted material  here s a Google book link to the page detailing the macros  The resulting script language can be found on page 324

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I once saw a macro package that would alias every C keyword to let you effectively program in Klingon   That s right  Klingon    Un fortunately  the project was abandoned and taken down several years ago

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define return if  std  random 1000   lt  2  throw std  exception    else return   this is just so evil  It s random  which means it fires in different places all the time  it changes return statement  which usually have some code on it that could fail all by itself  it changes innocent looking keyword that you won t ever get suspicious over and it uses exception from std space so you won t try to search through your sources to find it s source  Just brilliant

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The driver code for an ASIC I used about 10 years ago had a lot of sections that looked like   int foo state t  state        int a  b  rval             if  state- gt thing    whatever                      do whatever state                more code            return rval      After a lot of head scratching we finally found the definition    if DEBUG  define   dolog   s  d     FILE      LINE      else  define    endif   This was hard to find  because none of the source files that used it had any include files  There was a file called top c source file that looked like    include  lt namechanged h gt   include  lt foo c gt   include  lt bar c gt   include  lt baz c gt    Sure enough  this was the only file referenced in the Makefile  Whenever you changed anything  you had to recompile everything  This was  to make the code faster

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One fairly bad example    ifdef   cplusplus  define class  vclass  endif   This allows a C structure that contains a member variable called class to be handled by a C   compiler   There are two headers with this construct in it  one of them also contains   undef class  at the end and the other doesn t

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At the time it seemed like a good idea to  pass  a macro as an argument into another macro     I just couldn t stand the thought of defining a list of values in multiple places    The code here is contrived  and not very motivating   but gives you the idea    define ENUM COLORS CallbackMacro        CallbackMacro RED          CallbackMacro GREEN        CallbackMacro BLUE                  define DEFINE COLOR TYPE CALLBACK Color        Color   enum MyColorType       ENUM COLORS DEFINE COLOR TYPE CALLBACK      void RegisterAllKnownColors void     define REGISTER COLOR CALLBACK Color        RegisterColor Color   Color        ENUM COLORS REGISTER COLOR CALLBACK     void RegisterColor MyColorType Color  char  ColorName

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Raymond Chen has a really good rant against using flow control macros  His best example is straight from the original Bourne shell source code   ADDRESS alloc nbytes      POS     nbytes        REG POS rbytes   round nbytes BYTESPERWORD BYTESPERWORD        LOOP    INT     c 0      REG BLKPTR  p   blokp      REG BLKPTR  q      REP IF  busy p          THEN    WHILE  busy q   p- gt word  DO p- gt word   q- gt word OD         IF ADR q -ADR p   gt   rbytes         THEN    blokp   BLK ADR p  rbytes               IF q  gt  blokp             THEN    blokp- gt word   p- gt word              FI             p- gt word BLK Rcheat blokp  BUSY               return ADR p 1            FI         FI         q   p  p   BLK Rcheat p- gt word  amp  BUSY       PER p gt q ORF  c     0 DONE     addblok rbytes       POOL

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include  lt iostream gt   define public static void main x  int main    define System out println x  std  cout  lt  lt  x  lt  lt  std  endl  public static void main String   args      System out println  Hello World

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Found in declarations  to much confusion    NON ZERO BYTE         Fixed 8   Constant  79 X     Found later    IF WORK AREA INDEX    ZERO BYTE THEN     found zero byte        WORK AREA INDEX    NON ZERO BYTE      reset to nonzero

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define private public

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Related to Raymond s rant is the following horrible  in my opinion  of course  macro    define CALL AND CHECK func  arg        int result   func arg               if 0    result                                                              sys exit -1                                                       I was pretty new to the practice of using macros and used this macro  but I expected the function that I passed to it to fail  And I was doing it in a background thread  so it stumped me for days why my entire app was  crashing    As an aside  if only std  tr1  function was around when this macro was written  I would have a week of my life back

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Real-world   MSVC has macros in minmax h  called max and min  which cause a compiler error every time I intend to use the standard std  numeric limits lt T gt   max   function

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define TRUE 0    dumbass   The person who did this explained himself some years later - most  if not all  C library functions return 0 as an indication that everything went well  So  he wanted to be able to write code like   if  memcpy buffer  packet  BUFFER SIZE     TRUE         rape that packet     Needless to say  nobody in our team  tester or developer  ever dared to glance at his code again

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Any macro that uses the token concatenation operator      I saw one that a colleague of mine had the pleasure of working with   They tried to make a custom-implementation of string interning  so they re-implemented strings using a massive number of macros that  of course  didn t work properly   Trying to figure out what it did made my eyes explode because of all the    s scattered about

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Be gentle  I wrote this as the only way I can think of to generically capture exceptions     I use it to capture and stop exceptions from propagating out of my public interface functions         Catch all generic exceptions and log appropriately      Logger is insulated from throwing  so this is a NO THROW operation   define CatchAll  msg         catch  const Poco  Exception  amp e                         try  LogCritical  Logs System    std  string  e displayText     append  msg      catch      assert 0                    catch  const std  exception  amp e                          try LogCritical  Logs System    std  string  e what     append  msg      catch      assert 0                    catch                           try  LogCritical  Logs System    std  string   Exception caught in     FUNCTION          append  msg      catch      assert 0                    I dislike the complexity and I hate macros  but how else would you  do  a generic catch handler   This isn t meant to be the end-all  this is just my generic catch handler to insulate legacy public functions and quickly add at least some level of protection when I know the function is getting invoked across a boundary which might throw up if a C   exception were to be thrown  your welcome  JNI    So does it make you run and hide  or is it the only way to do something like this   Basically     try     some block of code capable of throwing   CatchAll

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undef near  undef far   When I was new to game programming I was writing a frustum for a camera class is a game that I wrote  I had really strange errors in my code   It turns out that Microsoft had some  defines for near and far in windows h which caused my  near and  far variables to error on the lines that contained them  It was very difficult to track the problem down because  I was a newbie at the time  and they only existed on four lines in the whole project so i didn t realise right away

[c++] What is the worst real-world macros/pre-processor abuse you've ever come across?

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