How can I distinguish the use of a numerical value and the use of a #define with Clang?

Question

Lately I've been working with Clang, and for certain purposes, I need to know when a typedef macro is used.

As far as I know, both ast-dump for the following codes are exactly the same for the variable declaration :

#define SIZE_MAX 16
int my_array[SIZE_MAX]; 

and

int my_array[16]; 

AST-dump is the following :

VarDecl 0x1dbc370 <test.cpp:2:1, col:21> my_array 'int [16]'

Of course, I know that a typedef is just an alias, but when SIZE_MAX is parsed, there must be some kind of redirection to get the 16 value.

So, how can I distinguish when a macro is called, and when it is not ?

Answer 1

Yes, you can.

---

In Clang, the AST nodes are tagged with a SourceLocation which, as the description in the link implies, encodes both its spelling location and its instantiation location .

Therefore, using the SourceLocation of a node in combination with a SourceManager , you should not only be able to know whether something came from a macro-expansion, or not, but in case it does you should also be able to retrieve the expansion stack...

... which is what happens in diagnostics :

#define ARRAY_SIZE 0

int Array[ARRAY_SIZE] = {};

yields:

main.cpp:3:11: warning: zero size arrays are an extension [-Wzero-length-array]
int Array[ARRAY_SIZE] = {};
          ^~~~~~~~~~
main.cpp:1:20: note: expanded from macro 'ARRAY_SIZE'
#define ARRAY_SIZE 0
                   ^
1 warning generated.

Have a look at http://llvm.org/svn/llvm-project/cfe/trunk/lib/Frontend/DiagnosticRenderer.cpp and notably:

static StringRef getImmediateMacroName(SourceLocation Loc,
                                       const SourceManager &SM,
                                       const LangOptions &LangOpts) {
   assert(Loc.isMacroID() && "Only reasonble to call this on macros");
   // Walk past macro argument expanions.
   while (SM.isMacroArgExpansion(Loc))
     Loc = SM.getImmediateExpansionRange(Loc).first;

(copied verbatim, with the typo in the comment)