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class: not reading private variables

clonxy (22)
I need help with my assignment. Some of the objects in my cpp file isn't reading the private variables.

Map.h:
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#ifndef Map_h
#define Map_h
#include <iostream>
#include <vector>
#include <fstream>

class Map
{
  private:
  vector <vector<char> > map2d;
  int row;
  int col;
  int char_pos_row;
  int char_pos_col;

  public:
  Map(); //constructor, map size = 0
  Map(string filename); //loads txt from filename using fstream and creates a map
  void Display() const; //displays map, prints vector
  int Get(int row, int column) const; //method that returns the character at (row, column) position
  bool is_char_pos_possible(int r, int c);
  void Set(int row, int column, int new_value); //sets character from row,col to new value


  ~Map(); //deconstructor
};


#endif


Map.cpp:
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#include "Map.h"
#include <fstream>
#include <vector>
#include <string>
#include <iostream>


/*
user assert row > height; row >0
  Map(); //constructor
  Map(string filename); //loads txt from filename and creates a map
  int Display() const; //displays map
  int Get(int row, int column) const; //gets row, col of character pos
  void Set(int row, int column, int new_value); //sets character from row,col to new value

*/

Map::Map() //default constructor that creates size of 0
{
  int row = 0; //row/col for vector
  int col = 0;
  int char_pos_row = 0;
  int char_pos_col = 0;

	// vector<vector<char> > map2d(row, vector<char>(col,0));
}

Map::Map(std::string filename) //loads txt from filename and creates a map
{
  std::ifstream fs;
  fs.open(filename);

  //checks to see if file exists
  if (fs.fail())
  {
  std::cerr << "Opening file failed.\n";
  }
  int r,c;
  //inputs map into vector
  fs >> r;
  fs >> c;
  fs >> std::noskipws;

  row = r;
  col = c;

  map2d.resize(c, std::vector<char>(r));  
  map2d[row][col];

  for (int i = 0; i < row; i++)
  {
    fs.ignore(1);
    for (int j = 0; j < col; j++)
    {
      char ch;
      fs >> ch;
      map2d[i][j] = ch;
    } 
  }
  fs.close(); //finished
}

 void Display() //displays map
{
  std::cout << std::endl;

  for(int i = 0; i < row; i++)
  {
    for (int j = 0; j < col; j++)
    {
      std::cout << map2d[i][j];
    }
  std::cout << std::endl;
  }

}

char Get(int r, int c)//method that returns the character at (row, column) position
{
  for (int i = 0; i < row; i++)
  {
    for (int j = 0; j < col; i++)
    {
      if(map2d[i][j] == 'u')
      map2d[i][j] = ' '; //deletes old hero
    }
  }
  return map2d[r][c];
}

bool is_char_pos_possible (int r, int c) //is the character position possible?
{
  if (char_pos_row > r || r < 0)
  {
    return false;
  }
  else if (char_pos_col > c || c < 0)
  {
    return false;
  }
  else if (map2d[r][c] == '*')
  {
    return false;
  }
  else 
  {
    return true;
  }
}

void Set(int r, int c, int new_value)//sets character from row,col to new value
{
  if (is_char_pos_possible(r,c) == true)
  {
    int char_pos_row = r;
    int char_pos_col = c;
    map2d[r][c] = new_value;
  }

}

Map::~Map(){} //deconstructor
jonnin (11437)
display and get and others are not class members.

you need to to tie them back to the class via
Map::functionname( ...
Manga (1030)
Also watch for type matching... You have a function declaration int Get, and a function definition char Get.
clonxy (22)
Thanks,

I changed the objects and fixed the declarations.
Stewbond (2827)
The main problem is that you re-define members as locals. A local-definintion over-rides (for lack of a better word) the member definitions.

Your constructor:
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Map::Map() //default constructor that creates size of 0
{
  int row = 0; //row/col for vector
  int col = 0;
  int char_pos_row = 0;
  int char_pos_col = 0;

	// vector<vector<char> > map2d(row, vector<char>(col,0));
}


Does not actually initialize any members. It creates local variables, sets those to 0, and then releases those variables. That's why you don't seem to be able to read private members.

To initialize the members, change your constructor to this: 
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Map::Map() //default constructor that creates size of 0
{
   row = 0; //row/col for vector
   col = 0;
   char_pos_row = 0;
   char_pos_col = 0;
}


You have the same problem in your Set method.

Your next question may be: "But how do I know if it's a member or local?" A common solution is to use a naming convention. Using "m_" as a prefix, or simply "_" as a postfix is a good way to do it.

Oh, and one more thing... You've declared Display, Get, and Set as methods, but you've defined them as functions. Be sure to use the Map:: before the function name (after the return value) for those definitions.
Last edited on
Ganado (6809)
A local-definintion over-rides (for lack of a better word) the member definitions.
The better word would be that it "shadows" a variable.
https://en.wikipedia.org/wiki/Variable_shadowing

Just FYI.
clonxy (22)
Thank you Stewbond, that was really helpful. I made the changes. Currently, I'm having an issue copying map.txt into the 2d vector. I made a new post for it here: http://www.cplusplus.com/forum/beginner/240663/

I made the appropriate changes and I'll post it for other users who may be interested in it in the future:

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//David Chen
//Home Project 8

#include "Map.h"
#include <iostream>
#include <fstream>

/*
This was coded for the map below (assuming '*' = wall, 'u' = hero):

9
5
*********
**   ****
** ******
** u  ***
*********

  Map(); //constructor
  Map(string filename); //loads txt from filename and creates a map
  int Display() const; //displays map
  int Get(int row, int column) const; //gets row, col of character pos
  void Set(int row, int column, int new_value); //sets character from row,col to new value

*/

Map::Map() //default constructor that creates size of 0
{
  row = 0; //row/col for vector
  col = 0;
  char_pos_row = 0;
  char_pos_col = 0;
}

Map::Map(std::string filename) //loads txt from filename and creates a map
{
  std::ifstream fs;
  fs.open(filename);

  //checks to see if file exists
  if (fs.fail())
  {
  std::cerr << "Opening file failed.\n";
  }

  //inputs map into vector
  int r,c;
  std::cout << "map:" << std::endl;
  fs >> c;
  fs >> r;
  fs >> std::noskipws;
  fs.ignore(1);

  row = r;
  col = c;

  map2d.resize(c, std::vector<char>(r));  
  map2d[row][col];


/*
5x9
*********
**   ****
** ******
** u  ***
*********
*/

  for (int i = 0; i < row; i++)
  {
    for (int j = 0; j < col+1; j++)
    {
      char ch;
      fs >> ch;
      map2d[i][j] = ch;
    
      // std::cout << ch;
    } 
  }
  fs.close(); //finished
}

void Map::Display() const//displays map
{
  std::cout << std::endl;

  for(int i = 0; i < row; i++)
  {
    for (int j = 0; j < col; j++)
    {
      std::cout << map2d[i][j];
    }
  std::cout << std::endl;
  }

}

char Map::Get(int r, int c)//method that returns the character at (row, column) position
{
  for (int i = 0; i < row; i++)
  {
    for (int j = 0; j < col; i++)
    {
      if(map2d[i][j] == 'u')
      map2d[i][j] = ' '; //deletes hero's old position.
    }
  }
  return map2d[r][c];
}

bool Map::is_char_pos_possible (int r, int c) //is the character position possible?
{
  if (char_pos_row > r || r < 0)
  {
    return false;
  }
  else if (char_pos_col > c || c < 0)
  {
    return false;
  }
  else if (map2d[r][c] == '*')
  {
    return false;
  }
  else 
  {
    return true;
  }
  for (int i = 0; i < row; i++)
  {
    for (int j = 0; j < col; j++)
    {
      if (map2d[r][c] == '*') //checks to see if char is trying to stand on the wall.
      {
        return false;
      }
    }
  }
}

void Map::Set(int r, int c, int new_value)//sets character from row,col to new value
{
  if (is_char_pos_possible(r,c) == true)
  {
    char_pos_row = r;
    char_pos_col = c;
    map2d[r][c] = new_value;
  }

}

Map::~Map(){} //deconstructor
Last edited on
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