struct - Why token concatenation doesn't work in C++? -

i have following piece of code , want programmatically access fields of struct:

#include <stdio.h> #include <stddef.h>  #define field(name, num)  {name##num}   struct sfoo {     int i;     float   f1;     float   f2;     char    c; };  int main() {     printf("offset of 'f1' %u", offsetof(sfoo, f1));     printf("offset of 'f1' %u", offsetof(sfoo, field(f, 1))); } 

the first line in main() works second line doesn't compile (msvc 2012). how can generate field name using token concatenation?

get rid of { , } in definition of field.

#define field(name, num)  name##num 

with previous definition, print statement expand offsetof macro won't accept:

    printf("offset of 'f1' %u", offsetof(sfoo, {f1}));