Re: [Swig-user] std::auto_ptr and reference counted pointers in Java

[William S F. <ws...@fu...>]

Steven Sharp wrote:
> While searching the lists for info on using std::auto_ptr and
> reference counted pointers, I came across wsf's typemap for auto_ptr. 
> I extended for Java directors thus:
> 
> //%define SWIG_AUTO_PTR_TYPEMAPS(PROXYCLASS, TYPE...)
> %define SWIG_AUTO_PTR_TYPEMAPS(PROXYCLASS, TYPE, PROXYPKG...)
> .
> .
> .
> %typemap(directorin,descriptor="PROXYPKG/PROXYCLASS;") std::auto_ptr< TYPE > %{
>     jlong lpp = 0;
>     *(TYPE**)(void *) &lpp = $1.release();
>     $result = lpp;
> %}
> %typemap(javadirectorin) std::auto_ptr< TYPE > {
>     long cPtr = $jniinput;
>     return (cPtr == 0) ? null : new PROXYCLASS(cPtr, true);
> }
> %typemap(javadirectorout) std::auto_ptr< TYPE >
> "PROXYCLASS.getCAutoPtr($javacall)"
> 
> This *seems* to work as I haven't had a segfault yet.  Is there any
> way to concatenate things in the descriptor of the directorin?  I was
> hoping to use "LPROXYPKG" but obviously that won't work.  The
> work-around is that I'm passing "Lfoo" for the package.  What is the
> significance of "..." after TYPE?  I'm using them on PROXYPKG but
> without a good knowledge of how I may be borking the code.
> 
> Also, the code I'm working with is rife with reference counted "smart"
> pointers.  I was having problems with the reference going out of scope
> and deleting the referenced object.  The smart pointer is passed into
> a director method as a reference, which is then turned into a pointer.
>  I hand modified this code to copy construct a new smart pointer and
> pass that as the CPtr instead.  It seems to be working but I haven't
> done a memory leak check yet.  It looks like when the Java object is
> GCed that the smart pointer's reference count is decremented as well.
> 
> Is there an easier way to do this?  A way to tell swig/directors that
> it should copy an parameter object instead of creating a pointer to
> it?  Some flag I've missed?
> 

I don't have time to look at this in detail, but I can't see anything 
obviously wrong with it.

The %define is just like a C #define with main difference that it is a 
multiline define. The macro supports varargs, thus the "...". This is 
useful for when the C++ type contains commas such as in templates. So 
you can use the macro, eg:

SWIG_AUTO_PTR_TYPEMAPS(VectorPairDouble, vector<pair<double, double> >)

so you need to change your definition by swapping TYPE and PROXYPKG. 
With regard to concatenating strings in the descriptor, use normal macro 
macro concatenation like you would in a C macro.

BTW the extra (void *) cast has been removed from all SWIG typemaps as 
it suppresses a useful aliasing warning in some versions of gcc, see 
CHANGES files.

William