无效写入 valgrind 导致分段错误

Question

I am trying to create a maze class that can read an input stream that has the description of the maze and return a maze. However when I run a test with this given input stream:

20 10
####################
#................<.#
#..................#
#...###............#
#.....#............#
#.....#............#
#...###............#
#..................#
#..................#
####################

It gives a segmentation fault, and I run the object file on valgrind to check what is happening:

Invalid write of size 8
==2482545==    at 0x4032CD: Maze::setTile(Position const&, Tile*) (maze.cpp:47)
==2482545==    by 0x40347B: Maze::read(std::istream&) (maze.cpp:67)
.....
==2482545==  Address 0x0 is not stack'd, malloc'd or (recently) free'd

I don't really understand why there is an segmentation fault or an invalid write, in my code, I should have allocated the space for each tile inside my setTile function, so there should be space for me to write. I also stacked the tile_collection with my constructor so tile_collection should be initialized when I called Maze(20,10), and the resizing inside setTile should be working. Can you please point out what am I missing? Thank you in advance. I know that I asked a really similar question 3 hours ago but I am still stuck on this invalid write.(The Position class and tilefactory class are 2 given files so they should work fine) This is the class declared in header file:

class Maze {
private:
  // TODO: add fields
  int Width;
  int Height;
  std::vector<Tile*> tile_collection;

This is my cpp file:

Maze::Maze(int width,int height):
  Width(width),Height(height){
  tile_collection[(width-1)*(height)];
}

}


void Maze::setTile(const Position &pos,Tile *tile){
  tile_collection[pos.getX()+pos.getY()*(Width)]=tile;
}


Maze *Maze::read(std::istream &in){
  int x;int y;char c;
  if ((in>>x)&&(in>>y)){
      Maze *new_maze=new Maze(x,y);
      //loop over the specified maze dimension
        for (int i=0;i<y;i++){
          for (int j=0;j<x;j++){
            if (in>>c){
              //using tilefactory to change character into a tile
              TileFactory *fac=TileFactory::getInstance();
              Tile* temp=fac->createFromChar(c);
              //if createFromChar fails, return nullptr, otherwise set tile at position j,i
              if (temp==nullptr){
                return nullptr;
              }
              else{
                new_maze->setTile(Position(j,i),temp);
              }
            }
          }
        }
        return new_maze;
  }
  else{
    return nullptr;
  }
}

Answer 1

I suspect that the fault you are seeing is a consequence of this line:

          TileFactory *fac=fac->getInstance();

You're declaring a local pointer-variable named fac but you are trying to call a method ( getInstance() ) through that same pointer-variable before it's even been set to anything. Seems like a recipe for disaster to me!