Some examples of string operations in C preprocessor

1. /*
2.     Some rabbits
3. */
4. #define HELLO hello
5. #define A 0xDEADBEAF
6. #define B A
7. #define C B
8. #define N
9. #undef U
10.     
11. /*
12.     More rabbits (female this time)
13. */
14. #define CONCAT(x,y) x ## y
15. #define STRINGIFY(x) #x
16. #define STRINGIFY_DEF(x) STRINGIFY(x) /* Interesting rabbit */
17.     
18. /*
19.     Let's make an EXPERIMENT!!!
20. */
21. #define X1 STRINGIFY("str")
22. #define X2 STRINGIFY(A)
23. #define X3 STRINGIFY(B)
24. #define X4 STRINGIFY(C)
25. #define X5 STRINGIFY(N)
26. #define X6 STRINGIFY(U)
27.     
28. #define X11 STRINGIFY_DEF("str")
29. #define X12 STRINGIFY_DEF(A)
30. #define X13 STRINGIFY_DEF(B)
31. #define X14 STRINGIFY_DEF(C)
32. #define X15 STRINGIFY_DEF(N)
33. #define X16 STRINGIFY_DEF(U)
34.     
35. #define X101 STRINGIFY(CONCAT(a, b))
36. #define X102 STRINGIFY(CONCAT(A, N))
37. #define X103 STRINGIFY(CONCAT(HE, LLO))
38. #define X104 STRINGIFY_DEF(CONCAT(HE, LLO))
39.  
40. #include <stdlib.h>
41. #include <stdio.h>
42.  
43. #define PRINT_STR(expr) printf(#expr " = %s\n", expr);
44.  
45. int main() {
46.     PRINT_STR(X1);
47.     PRINT_STR(X2);
48.     PRINT_STR(X3);
49.     PRINT_STR(X4);
50.     PRINT_STR(X5);
51.     PRINT_STR(X6);
52.  
53.     PRINT_STR(X11);
54.     PRINT_STR(X12);
55.     PRINT_STR(X13);
56.     PRINT_STR(X14);
57. #ifdef __GNUC__
58.     PRINT_STR(X15); /* Won't work in MSVC */
59. #endif
60.     PRINT_STR(X16);
61.  
62.     PRINT_STR(X101);
63.     PRINT_STR(X102);
64.     PRINT_STR(X103);
65.     PRINT_STR(X104);
66. }

* This source code was highlighted with Source Code Highlighter.

MS VC++ outputs:
X1 = "str"
X2 = A
X3 = B
X4 = C
X5 = N
X6 = U
X11 = "str"
X12 = 0xDEADBEAF
X13 = 0xDEADBEAF
X14 = 0xDEADBEAF
X16 = U
X101 = CONCAT(a, b)
X102 = CONCAT(A, N)
X103 = CONCAT(HE, LLO)
X104 = hello 

GCC outputs:
X1 = "str"
X2 = A
X3 = B
X4 = C
X5 = N
X6 = U
X11 = "str"
X12 = 0xDEADBEAF
X13 = 0xDEADBEAF
X14 = 0xDEADBEAF
X15 =
X16 = U
X101 = CONCAT(a, b)
X102 = CONCAT(A, N)
X103 = CONCAT(HE, LLO)
X104 = hello

STRINGIFY_DEF(N) causes problems:
GCC treats it as empty string ("") and MSVC treats it as just empty define ()