Garmaine Staff asked 3 months ago

I have a function in C++ that looks like:

//ellipsis are irrelevant variables. Not variadic
lint find_max(const void* ptr, ... , const vector<lint> &nums, ...)
{
    const mm (*arr)[nums.size()] = (const mm (*)[nums.size()]) ptr;
    //or
    const mm (*arr1)[nums.size()] = reinterpret_cast<const mm (*)[nums.size()]>
                                      (ptr);
}


The two casts produce an error with little detail as to why.

 error: cannot convert ‘const mm (*)[(<anonymous> + 1)]’ {aka ‘const min_and_max (*)[(<anonymous> + 1)]’} to ‘const mm (*)[(<anonymous> + 1)]’ {aka ‘const min_and_max (*)[(<anonymous> + 1)]’} in initialization
   42 |   const mm (*arr)[nums.size()] = (const mm(*)[nums.size()])ptr;
      |                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                                  |
      |                                  const mm (*)[(<anonymous> + 1)] {aka const min_and_max (*)[(<anonymous> + 1)]}

If I am not mistaken, both lvalue type and the corresponding cast is similar. For future reference, should I have more than 2 dimensions, how can I add them? I'm still an amateur in pointer manipulation so this will help alot.

EDIT for some reason this did not produce any errors:

typedef long long int lint;
typedef struct min_and_max
{
    lint min;
    lint max;
}mm;


const lint find_max(const void* ptr, int i, int j, const vector<lint> &nums, 
                    const vector<char> &ops)
{
    const int dim = nums.size();
    const mm (*arr)[dim] = reinterpret_cast<const mm (*)[dim]>
                                      (ptr);

    //algorithm which I haven't figured out yet.
    some_lint_value = arr[i][j].max + arr[i-232414][j+46846].min;

    return some_lint_value;
}

void caller(vector<lint> &nums, vector<char> &ops)
{
    mm arr[ops.size()][nums.size()]; //ISO variable size forbid warn

    //looped logic for solving the max/min value for an expression problem
    arr[i][j].max = find_max(arr, i, j, nums, ops);
}