函数返回指针到指针

请看下面的代码:

class SVMClassifier : public LibHAR
{
 public:
  ...
   //This is my function returning a pointer to pointer to svm_node structure
  svm_node** SVMFeatureExtraction(SkeData* inputData, int* pFrameNum, int* pFeatureNum, double wt);
  //This function calls SVMFeatureExtraction
  virtual bool FeatureExtraction(SkeData* inputData, const double* dataLabels = NULL, int labelNum = 0); //This function calls SVMFeatureExtraction
  ...
 private:
 svm_node** SVMNodes;
 int dataNum;
 ...
}
svm_node** SVMClassifier::SVMFeatureExtraction(SkeData* inputData, int* pFrameNum, int* pFeatureNum, double wt)
{
    *pFeatureNum = FEATURENUM;
    *pFrameNum = inputData->GetFrameSaved();
    svm_node** pNodes = new svm_node*[*pFrameNum];
    for (int i = 0; i < *pFrameNum; i++)
    {
        pNodes[i] = new svm_node[FEATURENUM + 1];
        for (int j = 0; j < FEATURENUM / 3; j++)
        {
            FEATURE_VEC* pVec = new FEATURE_VEC;
            if (!CalFeatureVector(inputData, i+1, j+1, pVec, wt))
                return NULL;
            pNodes[i][j*3].index = j*3 + 1;
            pNodes[i][j*3].value = pVec->x;
            pNodes[i][j*3 + 1].index = j*3 + 2;
            pNodes[i][j*3 + 1].value = pVec->y;
            pNodes[i][j*3 + 2].index = j*3 + 3;
            pNodes[i][j*3 + 2].value = pVec->z;
            delete pVec;
        }
        pNodes[i][FEATURENUM].index = -1;
        pNodes[i][FEATURENUM].value = 0;
    }
    return pNodes;
}
bool SVMClassifier::FeatureExtraction(SkeData* inputData, const double* dataLabels, int labelNum)
{
    CleanNodes();
    int n;
    SVMNodes = SVMFeatureExtraction(inputData, &dataNum, &n, actWeight);  //Error here!
        ...
}

类方法FeatureExtraction调用另一个方法SVMFeatureExtraction，该方法返回一个指向指针的指针。我认为指针指向的内存是在堆中动态分配的，因为它是由"new"创建的。但是当我调试程序时，SVMFeatureExtraction返回的地址不能成功地分配给SVMNodes (SVMNodes总是"NULL")，尽管pNodes的内容是正确的。谁能告诉我代码出了什么问题?

谢谢。