concatenating in a macro

From: Gergely Buday (gergoe_at_math.bme.hu)
Date: 09/27/04 

Date: 27 Sep 2004 12:34:47 -0700

Hi folks,

c++ faq lite writes:

However you need a double layer of indirection when you use ##.
Basically you need to create a special macro for "token pasting" such
as:

 #define name2(a,b) name2_hidden(a,b)
 #define name2_hidden(a,b) a ## b

Trust me on this --- you really need to do this! (And please nobody
write me saying it sometimes works without the second layer of
indirection. Try concatenating a symbol with __LINE__ and see what
happens then.) 

---
Now my code is 
#include <stdio.h>
 
#define MYMACRO(a,b) \
        a ## b
 
int main(int argc, char** argv)
{
  int MYMACRO(tmp, __LINE__) = 1;
  printf("%d\n", MYMACRO(tmp, __LINE__));
  return 0;
}
 
and it compiles (with g++) and runs smoothly. What does the faq author
talk about?
Thanks in advance
- Gergely

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