GNU Compiler Debug 'Level'

While browsing the various option switches for my compiler (GNU C++ 3.2.3 is supported by my organization for my given hardware configuration), I ran across this:

-glevel
   :
Level 3 includes extra information, such as all the macro definitions
present in the program. Some debuggers support macro expansion when
you use -g3.

I compiled a test program with a few macros (such as a loop, a if-then-else on an argument), then tried the commercial debugger TotalView, and GDB on the code compiled -g3. I didn't see any difference (macros were not expanded to their original code, I couldn't 'step into' the macros, etc.).

Anyone here had the experience of getting extra debugging 'features' using -g3 on GNU compilers?

From stackoverflow

• I have tried -g3 off and on since 1992 and I have never gotten it to do anything useful.

• Your question appears to imply that you don't understand what macros are. Of course you can't step into a macro.

  The -g3 is quite useful for "macro heavy" programs. Consider:

  int main()
  {
    int i;
    for (i = 0; i < 20; ++i) {
  #define A(x) case x: printf(#x "\n"); break
      switch(i) {
        A(1); A(2); A(3); A(4); /* line 7 */
  #undef A
  #define A(x) case 10+x: printf("10+" #x "\n"); break
        A(1); A(2); /* line 10 */
      }
    }
    return 0;
  }
  

  Without -g3, when you are stopped on line 7 or 10, you may have to search quite a lot for definition of A(), and there could be many such definitions, so you would then have to figure out which one is "current".

  With -g3, GDB can to do the heavy lifting for you:

  (gdb) b 7
  Breakpoint 1 at 0x4004cc: file m.c, line 7.
  (gdb) b 10
  Breakpoint 2 at 0x4004fc: file m.c, line 10.
  (gdb) r
  
  Breakpoint 1, main () at m.c:7
  7         A(1); A(2); A(3); A(4);
  (gdb) info macro A
  Defined at /tmp/m.c:5
  #define A(x) case x: printf(#x "\n"); break
  (gdb) c
  1
  2
  3
  4
  
  Breakpoint 2, main () at m.c:10
  10        A(1); A(2);
  (gdb) info macro A
  Defined at /tmp/m.c:9
  #define A(x) case 10+x: printf("10+" #x "\n"); break
  (gdb) q
  

  Don Wakefield : I *do* understand that you can't step into a macro. That was my attempt to understand the manual's weak explanation that "Some debuggers support macro expansion" for -g3. Anyway, thanks, your explanation shows what I can *really* do with -g3! You win the accepted answer cookie!