Question

I’ having a problem allocating a structure in a function. Here is the code(I’m currently using visual studio 2008):

    Mat3x3* ProdMat(Mat3x3 *m, Mat3x3 *n)
    {
   if(m == NULL || n == NULL)
   {
      cout << "\t[W] Cannot compute product of the two matrixes one or both are NULL." << endl;
      return NULL;
   }

   Mat3x3 *p; // product
   int i, j;
   float sum = 0;

   p = (Mat3x3*)malloc(sizeof(Mat3x3)); // <= Exp cannot be evaluated

   for(i = 0; i < 3; i++)
   {
    for(j = 0; j < 3; j++)
    {
        sum = 0;

        for(int k = 0; k < 3; k++)
        {
            float a = m->a[i][k];
            float b = n->a[k][j];
            sum += a * b;
        }

        p->a[i][j] = sum;
     }
   }

   return p;
    }

P contains a matrix with 9 entries. Here is the context in which the error is given:

    Mat3x3* compute_final_trans(Trans **transes) // compute product of all   transformation matrixes from right to left
    {
    int k_trans = 0, i, j;
    Mat3x3 *final_trans;

    if(transes == NULL)
    {
    printf("\t[E] Cannot compute sequence of NULL transformations.\n");
    return NULL;
    }

    final_trans = (Mat3x3*)malloc(sizeof(final_trans));

    for(i = 0; i < 3; i++)       // generate eye matrix
    for(j = 0; j < 3; j++)
    {
        if(i == j)
        {
            final_trans->a[i][j] = 1;
        }
        else
        {
            final_trans->a[i][j] = 0;
        }
    }

    while(transes[k_trans++]);

    for(i = k_trans - 2; i >= 0; i--)
    {
    final_trans = ProdMat(transes[i]->matrix, final_trans); // <= ERROR
    }

    return final_trans;
    }

Final trans is initialised as the eye matrix and transes have been succesfully computed before this step(before calling compute_final_trans). The while is used to retreieve the number of transformations that transes contains. At line:

    final_trans = ProdMat(transes[i]->matrix, final_trans);

ProdMat fails to allocate memory for p which is a pointer to a Mat3x3 structure.
perror suggests that there isn’t enough memory to allocate to the structure. However I’m only using 1GB of RAM(4GB in all).

Any help/suggestion/reference will be very much appreciated.

Sebi

Answer 1

malloc(sizeof(final_trans))

This is bad. You are only allocating enough space for a pointer, not space for an array.