get unread section of istringstream

Question

I have a test where I get characters out of an std::istringstream. I would like to get the section of the std::istringstream that was not read during the test. The std::istringstream::str() function returns the entire string, not just the unread section.

How do I get just this section of the string?

@MooingDuck Wouldn't this just read until.. the end of the line? (And not until the `eof` of the `istringstream`.) — dyp, Jul 13 '13 at 21:07
oops. `std::getline(mystringstream, rest_of_string, 0);` will read until it finds a NULL or EOF, which is closer. — Mooing Duck, Jul 13 '13 at 21:50

David G · Accepted Answer · 2013-07-13T23:10:42.560

4

Assuming you don't manually set the input position indicator before this line:

std::string unread = stream.eof()  ?  "" : stream.str().substr( stream.tellg() );

edited Jul 13 '13 at 23:10

answered Jul 13 '13 at 19:59

David G

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Will that work for all implementations of std::istringstream? – Graznarak Jul 13 '13 at 20:02
@Graznarak Yes, there nothing implementation specific here. – David G Jul 13 '13 at 20:05
@DyP I don't quite understand. I'm not using `rdbuf()->str()` which i know will return the entire string. – David G Jul 13 '13 at 20:15
@DyP Right, I was thinking about something else ;) – David G Jul 13 '13 at 20:23
@0x499602D2 This doesn't work with a std::istringstream with an empty string. At least it doesn't in VS2012. – Graznarak Jul 13 '13 at 20:42
@Graznarak Do you mean when the stream is declared as `stringstream stream("")`? – David G Jul 13 '13 at 20:43
@0x499602D2 Yes. Also, same failure when the entire input has been consumed. – Graznarak Jul 13 '13 at 20:49
You'll probably need a check for `-1`, as `tellg` returns that in some (these) cases. – dyp Jul 13 '13 at 20:55
@Graznarak Try `std::string unread = stream.tellg() == -1 ? stream.str().substr( stream.tellg() ) : "";` – David G Jul 13 '13 at 20:58
@0x499602D2 It appears to only happen when the entire input stream has been consumed and has returned eof(). I get a std::out_of_range exception from it, which matches expected exceptions from std::string::substr(). – Graznarak Jul 13 '13 at 21:00
@Graznarak See if using `stream.eof()` as the ternary condition instead of `.tellg() == -1` works. – David G Jul 13 '13 at 21:05
@Graznarak Please try my update. I made a mistake with my previous code. – David G Jul 13 '13 at 23:37

score 0 · Answer 2 · edited May 23 '17 at 11:49

The simplest way to do this I think is to push the read buffer of the istringstream to a string stream:

void test(std::istringstream& iss)
{
  /* Test code */
}

int main()
{
   std::istringstream iss;
   std::stringstream not_readed_buffer;
  std::string not_readed;

   test( iss );

   if( iss )
   {
       not_readed_buffer << iss.rdbuf();
       not_readed = not_readed_buffer.str();    
   }
}

Check this answer for a similar question

get unread section of istringstream

2 Answers2