[SOLVED] Question about public inheritance (C++)

Question

So I'm using OpenCV, and want to use the cv::Mat class. However I need to add some additional data points to the class. My (simple) idea was simply to create a new class, asMat, which inherits publicly from cv::Mat.
class asMat : public cv::Mat {
public:
int my_variable;
It 'works' in a sense, I can create a cv::Mat, static cast it to asMat, and use it in a few opencv functions, while also saving values into my_instant_name.my_variable.
However, I can't do the following:-
asMat inLeft(height,width,CV_8UC1);
Basically, I'm trying to call a particular constructor from cv::Mat. My understanding is that if I publicly inherit from cv::Mat I would also inherit all its functions. Do constructors work differently somehow (have to be explicitly specified)?
Last edited by ngoonee (2010-04-26 10:27:52)

Answer 1

ngoonee wrote:As I understand, the crashing comes because they objects are not the same 'size' in memory. Unfortunately my asMat objects will have to begin life as cv::Mat instants, probably need some wrapper code to convert them.
Some very common code for what I think your case is:
cv::Mat *crateMat(int width, int height)
asMat *myMat = new asMat(width, height); // This calls the constructor you make that actually calls cvMat( height, width, CV_8UC1)
// some operations in asMat but not in cvMat
return myMat;
or
bool crateMat(cv::Mat *mat, int width, int height)
asMat *myMat = new asMat(width, height); // This calls the constructor you make that actually calls cvMat( height, width, CV_8UC1)
// some operations in asMat but not in cvMat
mat = myMat;
return true; // or false based on your operations
or if you just want to construct and not call functions only in asMat:
cv::Mat *mat = new asMat(width, height);
If you use the functions just be sure to clean up the pointers.  Also, as jdarnold said, do not use static cast the way you are.  This is what dynamic_cast is for:
bool doSomethingOnlyAsMatCanDo(cv::Mat *mat)
asMat *myMat = dynamic_cast<asMat*>(mat);
if (myMat)
// some operations in asMat but not in cvMat
return true;
return false;