Save and read multiline text as-is

[goforit22123-netizen]

I need to save text data to a YAML file exactly as it is, so that another program can subsequently read the file and transmit the data over the network without modification. At the same time, I need to maintain the YAML file's readability.

To preserve readability when saving the text data, I use the YAML::Literal manipulator.

The problem with this manipulator is that it strips all trailing newlines from the text, whereas I need to preserve them. Additionally, when reading the data back as a std::string, a newline character (\n) is appended to the end.

In other words, I need to save text data to YAML file exactly as is and be able to read it back exactly as is. Does yaml-cpp provide any mechanisms for this?

[SGSSGene]

Hi @goforit22123-netizen

your question is a little to unclear to give you a good answer.
Best would be to give a few lines of code and say what you would like the output to be.

Stripping whitespaces in many areas is part of the yaml spcification. To avoid stripping whitespaces you probably want to check out 8.1.1.2 Block Chomping Indicator

[goforit22123-netizen]

@SGSSGene
Hi!

I have following code:

YAML::Emitter out;
out << YAML::BeginMap;

out << YAML::Key << "text"
    << YAML::Value
    << YAML::Literal
    << "hello\nworld\n\n\n";

out << YAML::EndMap;

std::cout << out.c_str() << '\n';

And this code output is

text: |
  hello
  world

But |+ should be instead of |, like this

text: |+
  hello
  world

to preserve spaces when we read back the data

[sxrzh]

It seems that the current master branch has already fixed this, but the v0.9.0 latest release hasn't.

[goforit22123-netizen]

@sxrzh
Yes, but It works only for \n\n\n.
If we have \r\n\r\n\r\n at the end, it fails

[sxrzh]

According to YAML-spec 1.2.2 #5.4 :

Line breaks are interpreted differently by different systems and have multiple widely used formats.

[28] b-break ::=
    (
      [b-carriage-return](https://yaml.org/spec/1.2.2/#rule-b-carriage-return)  # x0A
      [b-line-feed](https://yaml.org/spec/1.2.2/#rule-b-line-feed)
    )                    # x0D
  | [b-carriage-return](https://yaml.org/spec/1.2.2/#rule-b-carriage-return)
  | [b-line-feed](https://yaml.org/spec/1.2.2/#rule-b-line-feed)

Line breaks inside scalar content must be normalized by the YAML processor. Each such line break must be parsed into a single line feed character. The original line break format is a presentation detail and must not be used to convey content information.

[29] b-as-line-feed ::=
  [b-break](https://yaml.org/spec/1.2.2/#rule-b-break)

Outside scalar content, YAML allows any line break to be used to terminate lines.

[30] b-non-content ::=
  [b-break](https://yaml.org/spec/1.2.2/#rule-b-break)

On output, a YAML processor is free to emit line breaks using whatever convention is most appropriate.

The parser must normalize \r\n into a single \n. I think this is important for ensuring a YAML file generated on Windows working well on Linux or other OS's.

If you truly want to preserve the \r character, I suggest using binary format rather than raw text.
Just like when you use fopen(..., "r") on Windows, \r\ns read will be replaced by \ns but when you use "rb" they will be preserved.

[sxrzh]

@goforit22123-netizen

[goforit22123-netizen]

@sxrzh
Thank you very much!
Anyway, master branch have some other issues related to LF at the end.
Please see #1502