Changing behaviour of double quotes when >> a stringstream

Question

Here is what I'm trying to do:

say I have a stringstream. Then I << "\"hello world\" today";

then when I do

sstr >> myString1 >> myString2;

I would like myString1 to have "hello world" and for myString2 to have "today"

Is there a way, possibly with a manipulator, to achieve this?

Thanks

Answer 1

Short Answer: No

Long Answer:
There are no manipulates that will do that for you.

Alternative Answer:

You could write your own type that could be used in conjunction with the stream operators do do this task.

#include <string>
#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>


class QuotedWord
{
    public:
        operator std::string const& () const { return data;}

    private:
        std::string     data;
      friend std::ostream& operator<<(std::ostream& str, QuotedWord const& value);
      {
        return str << value.data;
      }
      friend std::istream& operator>>(std::istream& str, QuotedWord& value);
      {
        char x;
        str >> x;
        if ((str) && (x == '"'))
        {
            std::string extra;
            std::getline(str, extra, '"');
            value.data = std::string("\"").append(extra).append("\"");
        }
        else
        {
            str.putback(x);
            str >> value.data;
        }
        return str;
      }
};

Then it can be used normally.

int main()
{
    QuotedWord  word;

    std::cin >> word;
    std::cout << word << "\n";

    // Easily convertible to string
    std::string tmp = word;
    std::cout << tmp << "\n"

    // because it converts to a string easily it can be used where string is needed.
    std::vector<std::string>   data;

    std::copy(std::istream_iterator<QuotedWord>(std::cin),
              std::istream_iterator<QuotedWord>(),

              // Notice we are using a vector of string here.
              std::back_inserter(data)
             );
}

> ./a.out
"This is" a test    // Input
"This is"           // Output
"This is"

Answer 2

No.

You either need to change the stream type (and hence the parsing semantics) or use your own string type (and hence change the parsing semantics in your overloaded op>>).

Instead, consider writing a function, similar to getline, which parses a possibly-quoted "word" out of a stream:

getqword(sstr, myString1);
getqword(sstr, myString2);
if (sstr) { /* both succeeded */ }

Note that input into a std::string already terminates at whitespace, so you only need to handle peeking ahead for a quote and then handle edge cases, of which there are plenty:

• escapes (quotes inside quotes)
  • the three prevalent styles are disallowed, backslash, and doubled quote; each has advantages and disadvantages
• spanning multiple lines (can \n be included?)
  • this is often a data error, so disallowing it can be a big help in some circumstances
• what happens if a quoted word ends next to another word?
  • "\"hello world\"today"
• skip leading whitespace?
  • unlike getline, it makes sense to honor the stream's skipws flag, but I could see that going the other way in rare circumstances
  • the istream sentry will handle this for you
• don't forget to use the stream's traits and locale, or use methods which already do that!
  • or document your assumptions

Answer 3

Not directly, you need a "wrapper" class that terminates where you want it to.

struct QuotedStringReader
{
   std::string& str;
   QuotedStringReader( std::string& s ) : str( s ) {}
};

std::istream operator>>( std::istream&, const QuotedStringReader& qsr );

std::string s, s2;
stream >> QuotedStringReader( s ) << s2;

Note that this is a rare occasion where you stream into a const - because you can write to the internal str even though it is const, and this way I can pass in a temporary.

Actually as you probably don't know what you are about to read you could simply call it "TokenReader" which reads whatever you define as a "token".

Answer 4

Nope. Not that particular way. You could create a "strong typedef" for string though and design a new operator>> for it that behaves that way.