通过 SWIG 从 Ruby 调用 C++ 函数

Question

I'm trying to call this function

bool process(const short* pPCM, size_t num_samples, bool end_of_stream = false);

from fplib part of the Last.FM FingerprintExtractor development at http://github.com/lastfm/Fingerprinter

I'm trying to call it from Ruby (1.9.2) going via SWIG (2.0.8).

This is my SWIG file so far

/* */
%define DOCSTRING
"This is a wrapper for The last.fm Fingerprint Extractor library."
%enddef
%module(docstring=DOCSTRING) FingerprintExtractor
%{
#include "../include/fplib/FingerprintExtractor.h"
%}
%include "typemaps.i"
%apply const short *INPUT { const short *pPCM };
%include "../include/fplib/FingerprintExtractor.h"

The output from swig -c++ -ruby FingerprintExtractor.i

FingerprintExtractor.i:10: Warning 453: Can't apply (short const *INPUT). No typemaps are defined.

I think the problem I'm having is a around the "const". Unfortunately I'm new to C++ and SWIG. I understand that the "const" forces the variable to be a constant, which is good practice in C++. But I can't figure out how to get SWIG to play ball. As per the message I need to define a typemap for the "const short *" declaration but for the life of me I can't figure it out.

Any help in figuring this out would be appreciated.

I've read the extensive documentation at http://www.swig.org/Doc1.3/Ruby.html which is sadly beyond my skills and whilst it covers aspects on pointers, arrays, constants, typedefs and typemaps I haven't been able figured out how all this relates to passing a pointer to an array when its declared as a const. I've have reviewed the C++ language to understand the requirement for the "const". I've tried to further understand the situation by looking at others implementations and of course I've googled it. Nothing specific enough turned up at a level I could understand. Hence my request for assistance.

Answer 1

Try adding:

%include "stdint.i"

underneath:

%include "typemaps.i"

stdint.i has typedefs for common types including short.