Question

I can’t figure out what I am doing wrong here.
I want to sort a list and have a compare function to sort it.
Found a code example where exactly my problem was solved but it doesn’t work for me.

I always get this error:
error: ISO C++ forbids declaration of ‘Cell’ with no type

Isn’t Cell my type?

AStarPlanner.h

class AStarPlanner {

public:

  AStarPlanner();

  virtual ~AStarPlanner();

protected:

  bool compare(const Cell& first, const Cell& second);

  struct Cell {

        int x_;
        int y_;
        int f_;   // f = g + h
        int g_;   // g = cost so far
        int h_;   // h = predicted extra cost

        Cell(int x, int y, int g, int h) : x_(x), y_(y), g_(g), h_(h) {
                f_ = g_ + h_;
        }
  };

};

AStarPlanner.cpp

 bool AStarPlanner::compare(const Cell& first, const Cell& second)
 {
    if (first.f_ < second.f_)
       return true;
    else
       return false;
 }

Answer 1

Move the declaration of Cell before the method declaration.

class AStarPlanner {
public:
  AStarPlanner();
  virtual ~AStarPlanner();
protected:
  struct Cell {
        int x_;
        int y_;
        int f_;   // f = g + h
        int g_;   // g = cost so far
        int h_;   // h = predicted extra cost
        Cell(int x, int y, int g, int h) : x_(x), y_(y), g_(g), h_(h) {
                f_ = g_ + h_;
        }
  };
  bool compare(const Cell& first, const Cell& second);
};

Also, technically, there’s no Cell type, but AStarPlanner::Cell (but it’s resolved automatically in the context of the class).