[mercury-users] Mercury and C

[Drirr C.]

Hello,

I'm writing a program using Mercury and C, however I haven't been able to
return a string from the c function.
 
I have something like this:
 
 :- pred buildPoly(int::in, int::in, int::in, int::in, string::out) is det.
 ...
:- pragma c_code(buildPoly(VARS::in,TERMS::in,NEG::in,SEED::in,OUT::out),
[may_call_mercury], "buildPoly(VARS,TERMS,NEG,SEED,OUT);").

 
 And then something like this:
 
 void  buildPoly(MR_Integer variables, MR_Integer terms, MR_Integer
negations, MR_Integer seed,  MR_Word result) {
 ...
     buffer = (char*)malloc(...);
 ...
     *((char **)result) = buffer;
}
 
As far as I understand from the documentation, Mercury passes an address
where the result must be put. However, "result" contains an invalid address
when buildPoly is called.
 
 And a result is only returned by the c function either when it can fail or
when it's a function (not a predicate), hence the void in buildPoly. Am I
right?
 
Any suggestions?
 
Thanks
Drirr C.

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