C/C++ Runtime Multidimensional Dynamic Array

Question

I have the following structure:

typedef struct _DynamicArray {
    int *data = nullptr;
    _DynamicArray *ptr_next = nullptr;
    _DynamicArray *ptr_dim = nullptr;
} DynamicArray; // so that every matrix cell contains another matrix cell

And then the following recursive method:

void _BuildArray(std::string const& source, StringIterator& sit, DynamicArray *dArray, bool& error) {
    if (!error) {
        while (sit+1 < source.length()) {
            ++sit;
            switch (source[sit]) {
                case '[':
                    dArray->ptr_dim = new DynamicArray();
                    _BuildArray(source, sit, dArray->ptr_dim, error);
                    break;
                case ']':
                    return;
                case ',':
                    break;
                case ' ':
                    break;
                default:
                    std::string str;
                    while (std::isdigit(source[sit])) {
                        str.push_back(source[sit]);
                        ++sit;
                    }
                    --sit;
                    if (str.empty()) {
                        error = true;
                        return;
                    }
                    else {
                        dArray->data = new int(stoi(str));
                        dArray->ptr_next = new DynamicArray();
                        dArray = dArray->ptr_next;
                    }
                    break;
            }
        }
    }
}

And then if I pass "[[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []]" as a parameter, it builds the following flatten: "[1,2,6,7,8]" (instead of "[1,2,3,4,5,6,7,8]"). Why?

The calling snippet is this:

StringIterator sit = 0;
bool error = false;
this->dynArray = new DynamicArray();
_BuildArray(this->listString, sit, this->dynArray, error);

I don't get it, you use std::string and then you want to complicate life yourself with raw pointers while you have so many facilities in C++ like std::list, std::vector.. — Jack
– Jack, Commented Jul 20, 2015 at 20:44
@Jack Anyway, how would you do that using std::list and std:vector (what would be the structure) ? — Andrejs Igumenovs
– Andrejs Igumenovs, Commented Jul 20, 2015 at 21:17

Jonathan Potter · Accepted Answer · 2015-07-20 20:44:49Z

1

Once your recursive _BuildArray call returns, you don't advance dArray like you do in the default: case. Meaning the next [ you encounter will overwrite the results of the previous [.

answered Jul 20, 2015 at 20:44

Jonathan Potter

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2 Comments

Andrejs Igumenovs Over a year ago

If I embed a trace if (dArray->data!=nullptr) {std::cout << "OVERWRITE\n";} before the dArray->data = new int(stoi(str));, it prints nothing.

Jonathan Potter Over a year ago

@AndrejsIgumenovs No you've misunderstood. Say you get [], []in the input string. It will allocate dArray->ptr_dim and recurse into the function, then return at the ]. The next [] does the same thing, overwriting the previous ptr_dim.

Jack · Accepted Answer · 2015-07-20 21:28:48Z

This answer is just to clarify my comment, I was talking about a structure which utilizes C++ STL structures to avoid having to manually manage allocations and dynamic memory, something like:

class CellVisitor
{
public:  
  virtual accept(Cell* cell) = 0;
};

class Cell
{
public:
  virtual void visit() = 0;

};

class ContainerCell : public Cell
{
private:
  std::vector<std::unique_ptr<Cell>> cells;

public:
  void addCell(...) { ... }

  void visit(CellVisitor* visitor) override
  {
    visitor->accept(this);
    for (auto& cell : cells)
      cell->visit();
  }
};

class IntegerCell : public Cell
{
private:
  std::vector<int> data;

public:
  void visit(CellVisitor* visitor) override
  {
    visitor->accept(this);
  }
}

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