C++ 从文件读取行时截断字符

Question

我知道这与 Windows 和 Linux 中的行尾指示符之间的差异有关，但我不知道如何解决它。

我确实看过这个帖子 Getting std :: ifstream to handle LF, CR, and CRLF?但是当我使用该帖子中的简化版本时(我使用直接读取而不是缓冲读取，知道存在性能损失，但现在想保持简单)，它并没有解决我的问题，所以我希望在这里得到一些指导。我确实测试了帖子的修改版本，它成功地找到并替换了我暂时用于测试场景的字符和选项卡，因此逻辑正常，但我仍然遇到问题。

我知道我在这里遗漏了一些非常基本的东西，当有人帮助我解决这个问题时，我可能会感到非常愚蠢，所以我宁愿不公开承认我的愚蠢，但我已经为此工作了一个星期，但无法解决它，所以我正在寻求帮助。

我是 C++ 新手，所以如果我在这里做的事情真的很菜鸟，请在回答时保持温和:-)

我创建了以下单文件程序来原型(prototype)化我想要做的事情。这是一个简单的例子，但我需要让它发挥作用才能更进一步。这不是一个家庭作业问题；而是一个问题。我真的需要解决这个问题才能创建一个应用程序。

程序(如下所示):

• 编译时没有错误或警告，并且在 CentOS 机器上干净地运行；

• 在 CentOS 机器上使用 mingw32 进行交叉编译，没有错误或警告，并且在 Windows 上干净地运行；

• 当我使用在 Linux 上创建的输入文本文件时，在 Linux 和 Windows 上生成正确的(预期)输出
• 当我使用在 Windows 中创建的输入文本文件时，不会产生正确的(预期)输出

所以，是的，它与 Linux 和 Windows 之间的不同文件格式有关，并且可能与换行代码有关，但我试图适应这一点，但它不起作用。

更复杂的是，我发现旧的 Mac 换行符又不同了:

• Linux =\n
• Windows =\r\n
• Mac =\r

.

请帮忙! ...

.

我想要:

1. 读入txt文件的内容
2. 对内容进行一些验证检查(此处未完成；下一步将进行)
3. 将报告输出到另一个txt文件

所以我需要检查文件，确定正在使用的换行符并进行相应处理

有什么建议吗？

我当前的(简化的)代码(尚未进行验证检查)是:

[代码]

int main(int argc, char** argv)
{
    std::string rc_input_file_name = "rc_input_file.txt";
    std::string rc_output_file_name = "rc_output_file.txt";

    char * RC_INPUT_FILE_NAME = new char[ rc_input_file_name.length() + 1 ];
    strcpy( RC_INPUT_FILE_NAME, rc_input_file_name.c_str() );
    char * RC_OUTPUT_FILE_NAME = new char[ rc_output_file_name.length() + 1 ];
    strcpy( RC_OUTPUT_FILE_NAME, rc_output_file_name.c_str() );

    bool failure_flag = false;

    std::ifstream rc_input_file_holder;
    rc_input_file_holder.open( RC_INPUT_FILE_NAME , std::ios::in );

    if ( ! rc_input_file_holder.is_open() )
    {
       std::cout << "Error - Could not open the input file" << std::endl;
       failure_flag = true;
    }
    else
    {
       std::ofstream rc_output_file_holder;
       rc_output_file_holder.open( RC_OUTPUT_FILE_NAME , std::ios::out | std::ios::trunc );

       if ( ! rc_output_file_holder.is_open() )
       {
          std::cout << "Error - Could not open or create the output file" << std::endl;
          failure_flag = true;
       }
       else
       {
          std::streampos char_num = 0;

          long int line_num = 0;
          long int starting_char_pos = 0;

          std::string file_line = "";
          while ( getline( rc_input_file_holder , file_line ) )
          {
             line_num = line_num + 1;
             long int file_line_length = file_line.length() +1 ;
             long int char_num = 0;
             for ( char_num = 0 ; char_num < file_line_length ;  char_num++ )
             {
                if ( file_line[ char_num ] == '\n' )
                {
                    if ( char_num == file_line_length - 1 )
                    {
                       file_line[ char_num ] = '-';
                    }
                    else
                    {
                       if ( file_line[ char_num + 1 ] == '\n' )
                       {
                          file_line[ char_num ] = ' ';
                       }
                       else
                       {
                          file_line[ char_num ] = ' ';
                       }
                    }
                }
             }

             int field_display_width = 4;
             std::cout << "Line " << std::setw( field_display_width ) << line_num << 
                    ", starting at character position " << std::setw( field_display_width ) << starting_char_pos << 
                    ", contains " << file_line << "." << std::endl;

             starting_char_pos = rc_input_file_holder.tellg();

             rc_output_file_holder << "Line " << line_num << ": " << file_line << std::endl;
          }

          rc_input_file_holder.close();
          rc_output_file_holder.close();
          delete [] RC_INPUT_FILE_NAME;
          delete [] RC_OUTPUT_FILE_NAME;
       }
    }

    if ( failure_flag )
    {
       return EXIT_FAILURE;
    }
    else
    {
       return EXIT_SUCCESS;
    }
}

[/代码]

相同的代码，有很多注释(为了我的学习经验)是:

[代码]

/*
 * The main function, from which all else is accessed
 */
int main(int argc, char** argv)
{


    /*
    *Program to:
    *  1) read from a text file
    *  2) do some validation checks on the content of that text file
    *  3) output a report to another text file
    */

    // Set the filenames to be used in this file-handling program
    std::string rc_input_file_name = "rc_input_file.txt";
    std::string rc_output_file_name = "rc_output_file.txt";

    // Note that when the filenames are used in the .open statements below
    //   they have to be in a cstring format, not a string format
    //   so the conversion is done here once
    // Use the Capitalized form of the file name to indicate the converted value
    //   (remember, variable names are case-sensitive in C/C++ so NAME is different than name)
    // This conversion could be done 3 ways:
    // - done each time the cstring is needed: 
    //          file_holder_name.open( string_file_name.c_str() )
    // - done once and referred to each time
    //     simple method: 
    //          const char * converted_file_name = string_file_name.c_str()
    //     explicit method (2-step):              
    //          char * converted_file_name = new char[ string_file_name.length() + 1 ];
    //          strcpy( converted_file_name, string_file_name.c_str() );
    // This program uses the explicit method to do it once for each filename
    // because by doing so, the char array created has variable length
    // and you do not risk buffer overflow
    char * RC_INPUT_FILE_NAME = new char[ rc_input_file_name.length() + 1 ];
    strcpy( RC_INPUT_FILE_NAME, rc_input_file_name.c_str() );
    char * RC_OUTPUT_FILE_NAME = new char[ rc_output_file_name.length() + 1 ];
    strcpy( RC_OUTPUT_FILE_NAME, rc_output_file_name.c_str() );

    // This will be set to true if either the input or output file cannot be opened
    bool failure_flag = false;

    // Open the input file
    std::ifstream rc_input_file_holder;
    rc_input_file_holder.open( RC_INPUT_FILE_NAME , std::ios::in );

    // Validate that the input file was properly opened/created
    // If not, set failure flag
    if ( ! rc_input_file_holder.is_open() )
    {
       // Could not open the input file; set failure flag to true
       std::cout << "Error - Could not open the input file" << std::endl;
       failure_flag = true;
    }
    else
    {
       // Open the output file
       // Create one if none previously existed
       // Erase the contents if it already existed
       std::ofstream rc_output_file_holder;
       rc_output_file_holder.open( RC_OUTPUT_FILE_NAME , std::ios::out | std::ios::trunc );

       // Validate that the output file was properly opened/created
       // If not, set failure flag
       if ( ! rc_output_file_holder.is_open() )
       {
          // Could not open the output file; set failure flag to true
          std::cout << "Error - Could not open or create the output file" << std::endl;
          failure_flag = true;
       }
       else
       {
          // Get the current position where the character pointer is at
          // Get it before the getline is executed so it gives you where the current line starts
          std::streampos char_num = 0;

          // Initialize the line_number and starting character position to 0
          long int line_num = 0;
          long int starting_char_pos = 0;

          std::string file_line = "";
          while ( getline( rc_input_file_holder , file_line ) )
          {
             // Set the line number counter to the current line (first line is Line 1, not 0)
             line_num = line_num + 1;


             // Check if the new line designator uses the standard for:
             //   - linux (\n)
             //   - Windows (\r\n)
             //   - Old Mac (\r)
             // Convert any non-linux new line designator to linux new line designator (\n)
             long int file_line_length = file_line.length() +1 ;
             long int char_num = 0;
             for ( char_num = 0 ; char_num < file_line_length ;  char_num++ )
             {
                // If a \r character is found, decide what to do with it
                if ( file_line[ char_num ] == '\n' )
                {
                    // If the \r char  is the last line character (before the null terminator)
                    //   the file use the old Mac format to indicate new line
                    //   so replace the \r with \n
                    if ( char_num == file_line_length - 1 )
                    {
                       file_line[ char_num ] = '-';
                    }
                    else
                    // If the \r char is NOT the last line character (before the null terminator)
                    {
                       // If the next character is a \n, the file uses the Windows format to indicate new line
                       //   so replace the \r with space
                       if ( file_line[ char_num + 1 ] == '\n' )
                       {
                          file_line[ char_num ] = ' ';
                       }
                       // If the next char is NOT a \n (and the pointer is NOT at the last line character)
                       //   then for some reason, there is a \r in the interior of the string
                       // At this point, I do  not know why this would be
                       //   but I don't want it left there, so replace it with a space
                       // Yes, I  know this is the same as the above action, 
                       //   but I left is separate to allow for future flexibility
                       else
                       {
                          file_line[ char_num ] = '-';
                       }
                    }
                }
             }


             // Output the contents of the line just fetched
             // This is done in this prototype file as a placeholder
             // In the real program, this is where the validation check(s) for the line would occur)
             //   and would likely be done in a function or class
             // The setw() function requires #include <iomanip>
             int field_display_width = 4;
             std::cout << "Line " << std::setw( field_display_width ) << line_num << 
                    ", starting at character position " << std::setw( field_display_width ) << starting_char_pos << 
                    ", contains " << file_line << "." << std::endl;

             // Reset the character pointer to the end of this line => start of next line
             starting_char_pos = rc_input_file_holder.tellg();

             // Output the (edited) contents of the line just fetched
             // This is done in this prototype file as a placeholder
             // In the real program, this is where the results of the validation checks would be recorded
             // You could put this in an if statement and record nothing if the line was valid
             rc_output_file_holder << "Line " << line_num << ": " << file_line << std::endl;
          }

          // Clean up by:
          //  - closing the files that were opened (input and output)
          //  - deleting the character arrays created
          rc_input_file_holder.close();
          rc_output_file_holder.close();
          delete [] RC_INPUT_FILE_NAME;
          delete [] RC_OUTPUT_FILE_NAME;
       }
    }

    // Check to see if all operations have successfully completed
    // If so exit this program with success indicated
    // If not,exit this program with failure indicated
    if ( failure_flag )
    {
       return EXIT_FAILURE;
    }
    else
    {
       return EXIT_SUCCESS;
    }
}

[/代码]

我拥有所有正确的包含内容，并且在针对 Linux 进行编译或针对 Windows 进行交叉编译时没有生成任何错误或警告。

我使用的输入文件只有 5 行(愚蠢的)文本:

A new beginning
just in case
the file was corrupted
and the darn program was working fine ...
at least it was on linux

Linux 上的输出正如预期的那样:

Line    1, starting at character position    0, contains A new beginning.
Line    2, starting at character position   16, contains just in case.
Line    3, starting at character position   29, contains the file was corrupted.
Line    4, starting at character position   52, contains and the darn program was working fine ....
Line    5, starting at character position   94, contains at least it was on linux.

当我导入在 Linux 中创建的文本文件时，Windows 中的输出是相同的，但是当我使用记事本并在 Windows 中手动重新创建相同的文件时，输出为

Line    1, starting at character position    0, contains A new beginning.
Line    2, starting at character position   20, contains t in case.
Line    3, starting at character position   33, contains e file was corrupted.
Line    4, starting at character position   56, contains nd the darn program was working fine ....
Line    5, starting at character position   98, contains at least it was on linux.

注意第 2、3、4 和 5 行起始字符位置的差异注意第 2,3 和 4 行开头缺少的字符

• 第 2 行缺少 3 个字符
• 第 3 行缺少 2 个字符
• 第 5 行缺少 1 个字符
• 第 5 行缺少 0 个字符

欢迎任何和所有的想法......

Answer 1

查看分辨率

cross-compiler out of date

为了解决这个问题，通过 apt-get install 安装的 mingw 交叉编译器已经过时了。当我手动安装更新的交叉编译器并更新设置以防止出现一些错误消息时，一切正常。