Re: C Interface Issue

[mcculloch]

If "extern" in C works when linked by plgc, I don't even need to pass the
pointer.   I'll try it.

Thanks,
John


Daniel Diaz-3 wrote:
> 
> Hi John,
> 
> The simplest way to pass pointers across Prolog and C is to store them
> into a global array t[] at index i and pass i as a Prolog integer.
> Obviously you can also directly store the structure in the array (this
> could avoid a malloc/free for the struct, but requires more memory if the
> array is large). The Prolog code receives an integer (which it does not
> use) and passes it back to another C code which recover i and uses t[i].
> 
> Did I miss something ?
> 
> Daniel
> 
> 
> Le 15 déc. 2012 à 22:05, mcculloch <address@hidden> a écrit :
> 
>> I've looked into various prologs and have decided Gnu Prolog is the
>> easiest
>> to interface to other systems via C routines.  However, there doesn't
>> seem
>> to be a good way to pass C struct pointers back to prolog for use by
>> other
>> foreign predicate calls implemented in C.  I think now maybe that might
>> not
>> be a good idea anyway.
>> 
>> The C interface I want to use creates a structure to represent a
>> connection
>> to a foreign system, and then requires this structure to subsequently
>> access
>> the system.  (For those who are curious, the system is mongoDB).  
>> 
>> One option is to create this structure, use it and destroy it every time
>> a
>> predicate is called that uses that system.  Obviously, this is very
>> inefficient.  The other option is to provide a predicate that returns the
>> connection structure back to prolog to provide to other predicates, but
>> this
>> is exactly what I can't figure out how to do in gprolog.
>> 
>> Any ideas would be greatly appreciated, and of course, any code that I
>> develop to completion will be shared.
>> 
>> John
>> 
>> 
>> Sorry this ended up in Bugs where it doesn't belong.  I'll try and figure
>> out how to move it.
>> 
>> 
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