【发布时间】：2015-04-16 17:04:47
【问题描述】：
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.我确实测试了我修改后的帖子版本，它确实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，所以逻辑是有效的，但我仍然有问题。
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周，并且无法解决，所以我正在寻求帮助。
我是 C++ 新手，所以如果我在这里做一些非常菜鸟的事情，请在回答时保持温和 :-)
我创建了以下单文件程序来原型化我想做的事情。所以这是一个简单的例子，但我需要让它更进一步。这不是作业问题；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）：
编译时不会出现错误或警告，并且可以在 CentOS 机器上干净地运行；
在 CentOS 机器上使用 mingw32 交叉编译没有错误或警告，并在 Windows 上干净运行；
- 当我使用在 linux 上创建的输入文本文件时，在 linux 和 Windows 上都产生正确的（预期的）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（预期的）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，但我已尝试适应它，但它不起作用。
为了更复杂，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：
- 读入一个txt文件的内容
- 对内容进行一些验证检查（此处未完成；接下来会进行）
- 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（还没有验证检查）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]
同样的代码，有很多 cmets（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]
我有所有正确的包含，当我为 linux 编译或为 Windows 进行交叉编译时没有产生错误或警告。
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 上的输出和预期的一样：
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，输出是
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 行的起始字符位置的差异 注意第 2,3 和 4 行开头的缺失字符
- 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
欢迎提出任何想法...
【问题讨论】：
-
Mac 自从 OSX 出来后就没有使用过 \r 了。现在它\n 就像大多数其他基于 Unix 的系统一样。
-
我查看了上面标识的链接，它使用了一个我还没有学习过的参考变量 (&)，所以我会深入研究并报告回来感谢您的快速回复..
-
@Ramblin 引用只是它们引用的变量的替代名称。尽管 C++11 的出现为它们增加了更多的力量，你可以在这里得到一个完整的解释：en.cppreference.com/w/cpp/language/reference 另外，如果在阅读完stackoverflow.com/questions/6089231/… 之后你有更多的问题可以在这里发布，我会尝试来回答，或者我们一起打开一个新问题。
-
谢谢乔纳森。我很快就会回到这个董事会。链接中的解决方案使用参考变量、输入缓冲区……我试图了解是否有一种更简单的方法（尽管速度较慢）我可以先理解字符串操作的概念，然后“毕业”到显示的精制解决方案。在这一点上，我试图理解链接中解决方案的思维/逻辑，但当然，我是在早上 6:00 之前和晚上 7:00 之后做的，所以点击速度不是很快:-) 正如麦克阿瑟所说。 .. “我会回来的！”。这可能需要一些时间:-)