Hi

I'm new to eigen, and fairly new to C++. As a result, I've hit a bit of a problem. I want to return a vector from a function, but I'm not really sure if it's even possible. I know that returning an array in C++ is a nasty business, but I wondered if there's a robust solution.

My current attempt throws up this error:
Unhandled exception at 0x770b15ee (ntdll.dll) in Test project 3.exe: 0xC0000005: Access violation writing location 0x00000000.

I have a class called cThinPlateSpline, which has the following method:

Code: Select all

VectorXf cThinPlateSpline::fvflGetHomolog(const MatrixXf& mflLandmarksIn, const MatrixXf& mflHomologsIn, const VectorXf& vflPoint)
{
  ...

  // Create the vector to return from the function
  VectorXf vflHomologOfPoint;
  vflHomologOfPoint.setZero();

  // Some maths to set the actual values of vflHomologOfPoint
  ...

  return vflHomologOfPoint;
}


I would like to return vflHomologOfPoint, but the above code doesn't work.

The main function looks like this:

Code: Select all

int _tmain(int argc, _TCHAR* argv[])
{
  // Initialise Nx2 floats matrix of landmark co-ordinates
  // Note: mflLandmarks = [x1 y1 (z1); x2 y2 (z2); ...; xn yn (zn)]
  MatrixXf mflLandmarks(4,2);

  // Initialise MxN floats matrix of homologous warped co-ordinates
  // Note: mflHomologs = [x1 x2 ... xn; y1 y2 ... yn; (z1 z2 ... zn)]
  MatrixXf mflHomologs(2,4);

  // Set up landmarks
  mflLandmarks <<  0,  1,
        -1,  0,
         0, -1,
         1,  0;

  // Set up homologs
  mflHomologs << 0,   -1,     0,    1,
       0.75, 0.25, -1.25, 0.25;
   
  cThinPlateSpline oTPS;
   
  VectorXf vflPoint;
  vflPoint <<  0.5,
              -0.5;

  VectorXf vflHomologOfPoint(2);
  vflHomologOfPoint << oTPS.fvflGetHomolog(mflLandmarks, mflHomologs, vflPoint);

  // Pause the output   
  cin.get();
 
  return 0;
}


Any help, or pointers (pun intended), would be much appreciated.

Thanks in advance.

Liam

You probably forgot to resize the vector vflHomologOfPoint. If you try it in "debug" mode, you should get a more explicit error message.

Thanks! You were right, I'd forgotten to resize the vector.

Liam