New line seen in command prompt but the same string is seen with \n in file output

Question

I have this code which runs fine

#include <iostream>
#include <set>
#include <sstream>

int main()
{   
    std::set<std::string> a;
    a.insert("foo");
    a.insert("bar");
    a.insert("zoo");
    a.insert("should");
    a.insert("work");
    std::stringstream b;
    std::set<std::string>::iterator it;
    for (it = a.begin(); it != a.end(); it++)
    {
        b << " " << *it <<"," <<"\n";

    }

    std::string aaa = b.str();
    std::cout <<aaa;
}

Output in command prompt:

bar, //new line after ","
foo, //new line after ","
should,
work,
zoo,

If I try to write the same string aaa in file I am expecting the same output to get print in the file i.e. every string after "," in new line, rather I am getting output in my file as follows (In single line with \n):

" bar,\n foo,\n should,\n work,\n zoo,\n"

Can anyone help me with this?

More Information on writing the string in file:

Here's how I am writing into file:

boost::property_tree::ptree pt1;
pt1.put( "Output", aaa );
boost::property_tree::write_json( "result.json", pt1 );

This will write JSON file, output of the above code in (Windows - NotePad/NotePad++) is as below:

{
    "Output": " bar,\n foo,\n should,\n work,\n zoo,\n"
}

Are you using windows or linux? sounds like a difference between line endings is the issue. — NathanOliver, Feb 06 '17 at 19:12
How are you opening the file to look at it? You shouldn’t see the quotation marks or the `\n`s if you open it in an editor. — Daniel H, Feb 06 '17 at 19:14
Post the code that writes it to a file, if that is what you are having a problem with. — , Feb 06 '17 at 19:27
@NathanOliver I am looking to get the output on both Linux & Windows. — silent_programmer, Feb 06 '17 at 19:39
Windows(`\r\n`) and linux(`\n`) support different type of line endings. Keep in mind. — jack jay, Feb 06 '17 at 19:41
May be @NeilButterworth is right, writing into file could be a problem. Let me edit the post with the code to write the file. — silent_programmer, Feb 06 '17 at 19:42
Use notepad++ instead of notepad. It handles this stuff much better. It will even tell you what kind of line ending the file has. — NathanOliver, Feb 06 '17 at 19:44
I already used **notepad++** and it show both window and linux file as the same — Shakiba Moshiri, Feb 06 '17 at 19:47
There's a lot of misinformation about line endings in these comments.... — Qix - MONICA WAS MISTREATED, Feb 06 '17 at 20:03
@LightnessRacesinOrbit Nathan Oliver's comment, upvoted +5, states that this is a line ending issue simply because it has to do with `\n`, even though it's been correctly pointed out this is a JSON issue and is expected behavior. File operations don't care about line endings in C++ (assuming you're using standard functionality). That's up to the application logic. Notepad++ wouldn't be showing `\r\n` and `\n` as the same because they aren't. And, as stated before, this isn't a line ending issue at all. — Qix - MONICA WAS MISTREATED, Feb 07 '17 at 00:00
@Qix: Nathan's comment is not information or misinformation about line endings, but guesswork about the question from before disambiguating information was added to it (before _anything_ about JSON was added to it, in fact). You're being unfair. _"Notepad++ wouldn't be showing \r\n and \n as the same because they aren't."_ Well, it does, actually; it shows them as a new line by detecting the file's line ending scheme when you open it. The distinction is thus hidden from the unsuspecting user. Anything else? — Lightness Races in Orbit, Feb 07 '17 at 00:02

score 3 · Answer 1 · answered Feb 06 '17 at 20:01

3

You are not writing a normal file! You are using a JSON library to write a file for you. And as it happens, in JSON strings, the end-of-line character is escaped just like in C source files, that is as "\n".

So, summing up, that is the expected behavior. If you want to get normal end-of-line characters, write a normal file, with fopen() and friends.

answered Feb 06 '17 at 20:01

rodrigo

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I am working on getting JSON as ouput, its easy to use boost library rather than creating a file. Is there any way normal EOL characters can be used with this Boost JSON library? – silent_programmer Feb 06 '17 at 20:04
@silent_programmer: Those requirements don't make sense, The LF character is not valid inside a JSON string, it must be encoded as `\n` (or `\u000a`). If you want to see your text divided in proper lines you could use a JSON viewer. I don't know of any but sure there are a few out there... A normal text editor will not show you that. – rodrigo Feb 06 '17 at 20:08
@silent_programmer: If the JSON theme is not a hard requirement, take a look at [this question](http://stackoverflow.com/questions/5257049/what-is-the-most-elegant-way-to-write-a-text-binary-file-with-c). – rodrigo Feb 06 '17 at 20:11
Thanks for the information but JSON is the requirement. – silent_programmer Feb 06 '17 at 20:24

score 1 · Answer 2 · answered Feb 06 '17 at 20:32

This is expected behaviour.

You are passing the string (which contains newlines) to a JSON library for encoding into JSON. That encoding step includes converting newlines to the substring "\n", because that's how we represent newlines inside strings in JSON.

Read more about JSON on the json.org website.

New line seen in command prompt but the same string is seen with \n in file output

2 Answers2