[Maya-Python] connect in MFnCompoundAttribute?

[miarmy]

hi!.my node has this attribute:

MFnCompoundAttribute compoundAttr;
MFnNumericAttribute numericAttr;

compoundsGRPAttr = compoundAttr.create("compounds", "comps");
compoundAttr.setArray(true);
indexAttr = numericAttr.create("index", "index", MFnNumericData::kInt, 0.0);

compoundAttr.addChild(indexAttr);

stat = addAttribute(compoundsGRPAttr);
if (!stat) { stat.perror("addAttribute"); return stat; }

now, i want run one function when, one plug, connected to indexAttr... how
can i do it? (c++ api)
and how i can connect the one node plug(the specified plug) to one of
indexAttrs?

Excuse me,I don't speak English as well as you....