[cfe-dev] #undefine cursors

Alexander Kornienko alexfh at google.com
Sun Nov 4 17:11:04 PST 2012

On Sat, Nov 3, 2012 at 2:43 PM, Matthieu Monrocq <matthieu.monrocq at gmail.com
> wrote:

> On Fri, Nov 2, 2012 at 10:34 PM, Iestyn Bleasdale-Shepherd <
> iestyn at valvesoftware.com> wrote:
>>  Hi,
>> When using the libclang API, ‘#define’ statements yield cursors, but
>> ‘#undefine’ statements do not.
>> Without a record of #undefines, I can’t determine which #defines are
>> extant at any given point in the code, and am thus unable to fully
>> determine dependencies between source files.
>> Is it possible to determine which #defines are active for a given source
>> location, or would the addition of #undefine cursors be a reasonable
>> feature request for the libclang API?
>> Thanks!
>> iestyn Bleasdale-Shepherd
> Well, you are lucky in that a good chunk of work went on recently into
> what was called "Macro History" whose goal is exactly to remember every
> single #define/#undef that a macro encountered in the pre-processing of the
> translation unit. Therefore, using this macro history, it should be
> possible to extract this information.
> Unfortunately, I do not know the exact API, Alexander Kornienko initiated
> the work on this, so he probably followed it, I have added him in CC so he
> can help us figure out exactly where this feature stands.
> -- Matthieu

Yep, there were a couple of related patches:

If you want to have a read-only access to macro history in libclang, you'll
probably need to forward these methods:
*), MacroInfo::getPreviousDefinition(), MacroInfo::getUndefLoc()

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