Re: istream replace

From:
Victor Bazarov <v.bazarov@comcast.invalid>
Newsgroups:
comp.lang.c++
Date:
Wed, 03 Dec 2014 16:43:57 -0500
Message-ID:
<m5o06d$pqs$1@dont-email.me>
On 12/3/2014 3:42 PM, Christopher Pisz wrote:

On 12/3/2014 2:34 PM, Victor Bazarov wrote:

On 12/3/2014 3:26 PM, Christopher Pisz wrote:

I need to replace any occurance of "\r\n" occurring in an istream with
just "\n".

I could so this by copying the stream contents to a string, then
replacing the occurances within the string, and creating another stream
object from that string.

Is there a more efficient way?


First you need to ask yourself, what is inefficient about it?
Second, why bother with creating another stream when you can simply
incorporate that action into your stream parser?

V


I'd figure the copies were inefficient. Although I know creating a
stringstream from a const string the docs say it just moves the
stringbuf pointer, I don't think the reverse works the same way. I could
be wrong.

But then, I don't even see how to create a string from an istream unless
it was a stringstream and I cast it, but I can't be sure what kind of
stream I am receiving as a parameter.

My parser orginally just worked with string, but then I made it work
with istream so that I could work with filestream and stringstream both
for on disk or in memory text. I did this just by fudging someone else's
3000 line unreadable chunk of poopy where they had taken a string and
created a stream and then used getline on it. It passed testing there,
so I didn't bother messing with it.

Now I come across the windows newline scenario in the data and have to
fix that.


OK, this is how I do it when I need to (and that's not often), use it if
you think it suits you, or maybe it'll give you an idea of your own.

I would extract the lines from the stream using std::getline and \n as
the delimiter. Once the line (a string) is in my possession, I check
whether it ends with \r\n (I don't remember if the delimiter is also put
in the string or not, if not then check for \r only), if so I simply
change the ending to remove \r and proceed with extracting the rest of
information from that string.

If you need multiple strings, then the next tool in the pipeline should
be the concatenator. If not, the parser.

Since you have the somebody's piece of code that already uses 'getline',
all you need to add is a small function to do the \r clean-up in each
line you get. Call your function right after 'getline' returns a string.

If you need more information, do ask.

V
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