Question

I’m facing some trouble to find the best way to return an struct with an array or pointer to an array.

here is what i want to do:
i have a struct

typedef struct {
    double *matrix;
    int cols;
    int rows;
    int nelems;
} ResultMat;

and a function that parses a file. I need to call that function and have it return the struct

ResultMat read (string file, string tag) {

  ResultMat mat;

  .....
  mat.cols = //some value from the file
  mat.rows = //some value from the file


  double array[rows][cols];
  //now i fill the array

  .......
  mat.matrix = *array;

  return mat;
}

within an array is filled with the values and i want to get back that whole struct with the
array/ pointer to the array stored in mat.matrix.

How to do that and is there maybe a better way? Im quite new to C and more familiar with OO programming, thats why I’m having trouble to find the best solution.

Hope anybody can give me some help! Thanks

Answer 1

I think that
double array[rows][cols];
will be a problem, as you create the array on the local function stack.
This will be erased once you leave the function.
You should also be aware of, that Variable-Length arrays are not ANSI-C conform and you should better not use it in my opinion.

You should work with pointers and dynamic memory allocation.
malloc would be the keyword here.

Hope this helps