C ++错误：IntilliSense标识符“ track”未定义-“可能未初始化的本地指针变量“ track””

Question

I'm trying to build a library of cvblob using OpenCV, and while compiling in VS 2013,

    error C4703: potentially uninitialized local pointer variable 'track' used
    error C4703: potentially uninitialized local pointer variable 'blob' used

I'm not sure why this is, since the pointer variables are defined a block above (albeit in a separate loop). Here is the code:

  // Update track
  //cout << "Matching: track=" << track->id << ", blob=" << blob->label << endl;
  track->label = blob->label; // ERROR HERE
  track->centroid = blob->centroid;

I'm using pre-written header and source files, so I'm not sure what the problem is. Anyone know what the fix is?

Before //Update Track , Here is where 'track' and 'blob' are referenced above, with no errors:

  // Select track
  CvTrack *track;
  unsigned int area = 0;
  for (list<CvTrack*>::const_iterator it=tt.begin(); it!=tt.end(); ++it)
  {
    CvTrack *t = *it;

    unsigned int a = (t->maxx-t->minx)*(t->maxy-t->miny);
    if (a>area)
    {
      area = a;
      track = t;
    }
  }

  // Select blob
  CvBlob *blob;
  area = 0; 

Answer 1

If the tt list is empty, or if it doesn't contain an element with the required area, then track will never be initialized. This is what the compiler complains about.

The function should probably only try to update the rack if it was actually found in the list of tracks.

The situation for blob is probably similar.

Answer 2

You should avoid declaring pointers without giving them a value. Hence you should replace the declaration with

CvTrack *track=NULL; (if you use C++ without the latest version) or
CvTrack *track=nullptr; (with C++11)

With this you're sure you will always give a value to your pointer (even if it's NULL). Then you should check before assigning anything if the pointer is NULL to avoid a runtime error.