[GiNaC-list] hash tables and sets

Richard B. Kreckel kreckel at ginac.de
Wed Oct 11 21:27:10 CEST 2006

Dear Marko,

Marko Riedel wrote:

>Someone hands me a chunk of memory through a void pointer, like so:
>    (void *)ptr.
>I want the memory pointed to by "ptr" to hold a newly initialized set
>of GiNaC expressions. How do I do this? How do I find out the number
>of bytes I will need? At some point in the future, someone will hand
>me that same pointer and I will want to free the set of expressions
>that it holds. Again, how do I do this?

Same as before. Don't let yourself be fooled by a funny long type name 
instead of a crisp "mystruct".

I suppose that should work (I haven't actually tested it):

    typedef std::set<GiNaC::ex, GiNaC::ex_is_less> myset;  // shorthand
    myset* inst;
    inst = (myset*)malloc(sizeof(myset));  // or get inst from elsewhere
    new(inst) myset;
    // do stuff to *inst here...
    delete inst;

Again: this is dirty stuff. But you wanted to do some interfacing. So be 


Richard B. Kreckel

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