The usage of "std::vector" in NX OPEN for C++ Programming

[robinjiang]

Source Code is following:
NXOpen::Features::FeatureCollection* f_collection = thePart->Features();
for (NXOpen::Features::FeatureCollection::iterator it=f_collection->begin();it != f_collection->end();it++)
{
NXOpen::Features::Feature* f11= (NXOpen::Features::Feature* ) *it;
std::vector<NXOpen::Features::Feature*> f_v;
f_v=f11->GetChildren();
if (f_v.size() > 0)
{
for (std::vector<NXOpen::Features::Feature*>::iterator it_sub=f_v.begin();
it_sub!=f_v.end();it_sub++)
{
NXOpen::Features::Feature* f22= (NXOpen::Features::Feature* ) *it;
}

}
}

The Compile and Link are both OK.When the project run to the row " f_v=f11->GetChildren(); " , "Access Violation" occured.
The code is mean to traverse the feature collection and get the children of each feature(if any).
Did i use the std::vector in a wrong way?