Weird bug while reading a file C++

user_13171776 0
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When I save the playingBoard array, save prints it properly, however when I try importing the file which save created with import, I get weird output - spaces get removed and replaced with 1s with no obvious logic. (examples are provided below)

minimal reproducible example:

#include <iostream>
#include <fstream>

class Board
{
public:
  char playingBoard[9][9];
  
  Board()
  {
    for (unsigned char i = 0; i < 9; ++i)
      for (unsigned char j = 0; j < 9; ++j)
        playingBoard[i][j] = ' ';
  }

  bool import(std::string filename)
  {
    std::ifstream ifs {filename};
    if (!ifs.is_open())
      return false;

    for (unsigned char i = 0; i < 9; ++i) {
      for (unsigned char j = 0; j < 9; ++j) {
        ifs >> playingBoard[i][j];
        std::cout << playingBoard[i][j] << "|";
      }
      std::cout << std::endl;
    }
  
    ifs.close();
    return true;
  }

  bool save(std::string filename) const
  {
    std::ofstream ofs {filename, std::ios::app};
    if (!ofs.is_open())
      return false;
  
    for (unsigned char i = 0; i < 9; ++i) {
      for (unsigned char j = 0; j < 9; ++j) {
        ofs << playingBoard[i][j];
        std::cout << playingBoard[i][j] << "|";
      }
      std::cout << std::endl;
    }
  
    ofs.close();
    return true;
  }
};

int main()
{
  Board board;
  board.import("filename");
  
  std::cout << std::endl;
  board.playingBoard[1][1] = '1';
  board.save("filename");
}

  • output on first run (file does not exist before, hence only one output):

     | | | | | | | | |
 |1| | | | | | | |
 | | | | | | | | |
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 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |

  • output on second run:

    1| | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |

1| | | | | | | | |
 |1| | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |

  • output on third run:

    1|1|1| | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |

1|1|1| | | | | | |
 |1| | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
file arrays c++
1 Answers

Your problem is that by default, whitespace is skipped with operator >>. You need to use another method of extracting the characters from your file such as the get member function (example below, tested with gcc-9.3.0).

  bool import(std::string filename)
  {
    std::ifstream ifs {filename};
    if (!ifs.is_open())
      return false;

    for (unsigned char i = 0; i < 9; ++i) {
      for (unsigned char j = 0; j < 9; ++j) {
        playingBoard[i][j] = ifs.get();
        std::cout << playingBoard[i][j] << "|";
      }
      std::cout << std::endl;
    }

Output:

$ ./a.out 
 | | | | | | | | |
 |1| | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |

 | | | | | | | | |
 |1| | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
 | | | | | | | | |
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user_2064040
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