Trouble with strucutures and pointers

Dear all,

I have two structures like this:

Code:

---

struct Matrix
{
  int r;
  int c;
  double * E;   
};


struct Model
{
    int n;
    int p;
    struct Matrix * pMx;
};

---

And a function which works on a struct matrix; it's prototype is:

Code:

---

double MxGetElement(struct Matrix * p, int iR, int iC)

---

This function works well if given a pointer to a Matrix structure.
I would like to call it through a "Model" pointer, let's call it "pModel".

I tried

Code:

---


x=MxGetElement((struct Matrix *) pModel->pMx, iR, iC);
x=MxGetElement(&(pModel->pMx), iR, iC);

---

etc etc and cannot make it work. Probably simple for you guys. I hope you can help me.

Many thanks,
D.

Your first line works. You will have to explain to us why you think it doesn't. (The cast is completely unnecessary, of course.)

Code:

---

x=MxGetElement(&Model.pMx, iR, iC);

---

[corrected it]

This should suffice:

Code:

---

x = MxGetElement(pModel->pMx, iR, iC);

---

If it does not, then the problem lies elsewhere.

Thanks for quick responses. This is a little odd to me.
My program works fine when I call it via a Matrix * directly, but it crashes when I go via Model *.
I have been using C for years for math purposes but never encountered this. How would I find the reason in this case?

D.

You are probably violating an assumption of the MxGetElement function. For instance, MxGetElement might assume that the pointer you pass it actually points to a valid piece of memory, but you pass it a NULL pointer instead.