函数返回指针指针

Question

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 ，它返回指向指针的指针。 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，虽然pNodes的内容是正确的，但SVMFeatureExtraction返回的地址无法成功分配给SVMNodes （SVMNode始终为“NULL”）。 谁能告诉我代码有什么问题？

谢谢。

Answer 1

这可能是一个愚蠢的建议，但你绝对肯定这一部分永远不会发生吗？

if (!CalFeatureVector(inputData, i+1, j+1, pVec, wt))
    return NULL;

Answer 2

*pFeatureNum = FEATURENUM;
    *pFrameNum = inputData->GetFrameSaved();
    svm_node** pNodes = new svm_node*[*pFrameNum];

这很奇怪，您尝试更改指针的值而不是指向的值。 为什么你通过指针传递两个参数并在函数中重新初始化它？

尝试这个：

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;

    }

Answer 3

试试这个（对@ Nagasaki的回答略有修改）：

*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];
...

（并且，如果它有效，接受@长崎的答案，我将对其进行编辑，以便获得信用）