c++ - 读取文件 C++ 时出现奇怪的错误

Question

当我保存 playingBoard 数组时，save 会正确打印它，但是当我尝试导入 save 使用 创建的文件时import，我得到奇怪的输出 - 空格被删除并替换为 1，没有明显的逻辑。 (示例如下)

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");
}

• 第一次运行的输出(文件之前不存在，因此只有一个输出):

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   |1| | | | | | | |
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• 第二次运行的输出:

  1| | | | | | | | |
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  1| | | | | | | | |
   |1| | | | | | | |
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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，operator >> 会跳过空格。您需要使用另一种方法从文件中提取字符，例如 get 成员函数(下面的示例，已使用 gcc-9.3.0 进行测试)。

  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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