Thread overview
File.byLine for either Windows / Unix newlines
Dec 11
Dennis
Dec 11
Dennis
December 11
I'm on Windows and I recently got confused by how Phobos functions handle newlines.

```
void main() {
    import std.stdio;
    import std.path : buildPath, tempDir;

    auto path = buildPath(tempDir(), "test.txt");
    auto file = new File(path, "w");

    file.write("hello there!\n");   //actually writes hello there!\r\n
    file.write('\n');               //actually writes \r\n
    file.rawWrite("\n");            //actually writes \n
    //file.rawWrite('\n');          //doesn't compile
    file.close();

    //byLine uses \n as default terminator, so a trailing \r is kept
    writeln(File(path).byLine.front~"huh?");   //prints "huh?o there!"
}
```

- Why do these functions behave like that?
- What is the easiest way to iterate over a file by line that works with both \r\n and \n line endings? I prefer not to write a new method for this.



December 11
On 12/11/17 10:40 AM, Dennis wrote:
> I'm on Windows and I recently got confused by how Phobos functions handle newlines.
> 
> ```
> void main() {
>      import std.stdio;
>      import std.path : buildPath, tempDir;
> 
>      auto path = buildPath(tempDir(), "test.txt");
>      auto file = new File(path, "w");
> 
>      file.write("hello there!\n");   //actually writes hello there!\r\n
>      file.write('\n');               //actually writes \r\n
>      file.rawWrite("\n");            //actually writes \n
>      //file.rawWrite('\n');          //doesn't compile
>      file.close();
> 
>      //byLine uses \n as default terminator, so a trailing \r is kept
>      writeln(File(path).byLine.front~"huh?");   //prints "huh?o there!"
> }
> ```
> 
> - Why do these functions behave like that?
> - What is the easiest way to iterate over a file by line that works with both \r\n and \n line endings? I prefer not to write a new method for this.

Please note that D uses FILE * as its underlying implementation. This means that whatever the C library does, D's library does.

In the case of Windows, there is this lovely concept that line endings should be \r\n, not just \n. So the C library helpfully inserts \r whenever it sees a \n. This is known as "text mode" as opposed to "binary mode".

rawWrite temporarily sets the mode to binary mode, then restores the original mode. This is why the \n is not translated there.

Here's the fun part: the default open mode is "rb". See the docs here: https://dlang.org/phobos/std_stdio.html#.File.this

So you are actually opening the file in binary mode, whereas you were writing it in text mode.

You can fix this in one of 3 ways:
1. Open your file for writing with "wb". This will not store the \r by default.
2. Open your file for reading with "r" (e.g. File(path, "r")). This will replace the \r\n with just \n in the underlying C library.
3. Stop using Windows ;)

-Steve
December 11
Thanks for your reply, that clears it up.

On Monday, 11 December 2017 at 21:13:11 UTC, Steven Schveighoffer wrote:
> 3. Stop using Windows ;)

Haha, if only the rest of the userbase would follow.