How to stringify an expression in C

Question

Is there a way to evaluate an expression before stringification in c?

example:

#define stringify(x)  #x
...
const char * thestring = stringify( 10 *          


        

Answer 1

You probably won't like the format in which the expression is going to be presented, yes, it is possible, but in a very eclectic way - you'd need to create a separate functional language that is being "run" by the preprocessor. The proof:

$ cvs -d:pserver:anonymous@chaos-pp.cvs.sourceforge.net:/cvsroot/chaos-pp login 
$ cvs -z3 -d:pserver:anonymous@chaos-pp.cvs.sourceforge.net:/cvsroot/chaos-pp co -P chaos-pp
$ cvs -z3 -d:pserver:anonymous@chaos-pp.cvs.sourceforge.net:/cvsroot/chaos-pp co -P order-pp
$ cd order-pp/example
$ grep -A 6 'int main' fibonacci.c
int main(void) {
   printf
     ("The 500th Fibonacci number is "
      ORDER_PP(8stringize(8to_lit(8fib(8nat(5,0,0)))))
      ".\n");
   return 0;
}
$ cpp -I../inc fibonacci.c 2>/dev/null | grep -A 6 'int main' 
int main(void) {
   printf
     ("The 500th Fibonacci number is "
      "139423224561697880139724382870407283950070256587697307264108962948325571622863290691557658876222521294125"
      ".\n");
   return 0;
}

In this example we have newly-made preprocessor-run purely functional language being used to calculate 500th Fibonacci number and then stringize it to give to C compiler.

Of course I very much doubt that this is something that you'd ever use in practice, and it is a very far stretched abuse of the preprocessor, but I consider it to be a very thought-provoking hack. (and yes, without the exotic theoretical twists like this one, it's not possible).