[cfe-dev] Extracting macro information using libclang, the C Interface to Clang

Mark inbox at akiwi.co.uk
Sun Nov 30 11:19:50 PST 2014

Hi Kevin,
Thanks for the info. Unfortunately, I'm in the same boat as you, 
deadlines to meet etc, no time to delve into the depths of libclang. 
Actually I tried to compile it with the preview version of visual studio 
2015 and failed miserably, lots of errors without time to investigate. 
(I want a 64-bit version of libclang.dll, not the 32-bit version that's 
supplied pre-compiled on windows).

I've partly hacked together something that does most of what I need 
using the token functions, but it's certainly not a permanent solution, 
and not even a full solution to the problem I described. I may hack on 
it some more to remove extra guff in the values, but that's about as far 
as I'll probably be able to take it without writing a macro parser.

void translateMacro( CXCursor cursor, Generator& model )
     std::string name;
     std::string value;
     CXToken* tokens    = nullptr;
     unsigned numTokens = 0;
     CXTranslationUnit transUnit = clang_Cursor_getTranslationUnit(cursor);
     CXSourceRange     srcRange  = clang_getCursorExtent(cursor);
     clang_tokenize( transUnit, srcRange, &tokens, &numTokens );
     for( unsigned n=0; n<numTokens; n++ )
         CXStringWrapper tokenText = clang_getTokenSpelling( transUnit, 
tokens[n] );
         if( n == 0 ) {
             name = tokenText.getStr();
             if( name[0] == '_' )
         else {
             CXTokenKind tokenKind = clang_getTokenKind( tokens[n] );
             if( tokenKind != CXToken_Comment )
                 const char* text = tokenText.getStr();
                 if( text && (text[0]!='#') && strcmp(text,"typedef") )
                     value += text;
     if( value.length() )
         Constant c;
         c.setName( name );
         c.setValue( value );
         model.addConstant( c );
     clang_disposeTokens( transUnit, tokens, numTokens );

Anyway, it seems there is a clear need for better preprocessing/macro 
functionality in libclang, so perhaps someone can add it to the C-API 
feature wish-list for future development?

Best regards,

On 2014-11-28 07:08, Kevin Funk wrote:
> On Thursday 27 November 2014 18:47:17 Mark wrote:
>> Hello all,
>> I'm new to libclang and using the Clang C-interface (version 3.6.0,
>> 222169) to parse some C header files.
>> My goal is to extract all the #define constants from the .h files.
>> For example, for the following #defines:
>> #define FEE 12
>> #define FIE 34
>> #define FOE (FEE+FIE)
>> #define FUM FIE
>> I would like to get both the names and the resulting raw values as follows:
>> FEE = 12
>> FIE = 34
>> FOE = 46
>> FUM = 34
>> I've got as far as handling /CXCursor_MacroDefinition, /and getting the
>> macro name from the cursor spelling. But after that, it's not clear to
>> me how I might obtain further information about the defined macro values
>> themselves.
> Yep. That's where we are as well. Getting the definitions + their uses is
> easy.
> Context: I'm the one working on (lib)Clang integration in KDevelop.
>> Is this possible using the libclang C interface?
>> If so, could someone please provide an example, or suggest an approach
>> that that might work?
> I was looking into this several months ago [1], too, and didn't find a
> solution so far. I'd love to get some API in libclang for achieving this.
> The open-source woboq code browser (code.woboq.org) has this feature, but uses
> C++-API of Clang; so it's definitely possible, but I still didn't find the
> time to map this implementation to libclang.
> Example usage:
>    http://code.woboq.org/qt5/qtbase/src/corelib/kernel/qobject.h.html#108,
>    hover over 'Q_OBJECT'.
> The code dealing with Clang's C++ API is here:
>    https://github.com/woboq/woboq_codebrowser/blob/master/generator/preprocessorcallback.cpp
> Note: If you're interested in getting this into libclang I'd be glad to help
> out!
> [1] http://lists.cs.uiuc.edu/pipermail/cfe-dev/2014-August/038543.html
>> Thank you,
>> Mark.

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