读取文件 C++ 时的奇怪错误

Question

当我保存playingBoard数组时，save正确打印它，但是当我尝试导入用save创build 的文件时import，我得到奇怪的输出 - 空格被删除并替换为1s 没有明显的逻辑。（下面提供了示例）

最小可重现示例：

#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");
}

• 第一次运行时的输出（文件之前不存在，因此只有一个输出）：

   | | | | | | | | |
   |1| | | | | | | |
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• 第二次运行的输出：

  1| | | | | | | | |
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   | | | | | | | | |
   | | | | | | | | |
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   | | | | | | | | |
   | | | | | | | | |
  
  1| | | | | | | | |
   |1| | | | | | | |
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   | | | | | | | | |
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   | | | | | | | | |
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• 第三次运行的输出：

  1|1|1| | | | | | |
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   | | | | | | | | |
  
  1|1|1| | | | | | |
   |1| | | | | | | |
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Answer 1

您的问题是默认情况下，空格会被跳过operator >>。您需要使用另一种从文件中提取字符的方法，例如get成员函数（下面的示例，使用 gcc-9.3.0 进行了测试）。

  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;
    }

输出：

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