Can I pass C++ strings into a method in the style of a stream?

Question

I'd like to do this:

MyClass mc = MyClass("Some string" << anotherString);

Thanks for your answers, I have decided to re-write this question based on what you've told me, as it's gotten a little messy. Eventually, I read C++ format macro / inline ostringstream, and decided to use a macro, as it's not really possible to do this using a constructor. Some answers my no longer be relevant.

Now, what I can actually, do is:

MY_CLASS("Some string" << anotherString << " more string!");

Using this macro:

#include <sstream>

#define MY_CLASS(stream) \
MyClass( ( dynamic_cast<std::ostringstream &> ( \
    std::ostringstream() . seekp( 0, std::ios_base::cur ) << stream ) \
) . str() )

Where the MyClass constructor takes a string:

MyClass::MyClass(string s) { /* ... */ }

Answer 1

Your compile error looks like have included

<iosfwd>

in your class's header file, but you haven't included

<sstream>

in the cxx file.

Answer 2

I think you should look at this question for some hints as to what will be required to get the behavior you want.

This sort of thing seems to a bit difficult.

Answer 3

The << operator returns an ostream &, not a streamstream &, so you'd have to do a dynamic cast:

MyClass::MyClass(ostream &stream)
{
    string myString = dynamic_cast<stringstream &>(stream.str());
}

stringstream s;
MyClass *mc = new MyClass(s << "Some string" << anotherString);

But really that's a terrible thing to do. Try something like this:

class Streamer
{
stringstream stream;
public:
    template <class T>
    Streamer &operator <<(const T &object) { stream << object; return *this;}
    operator string() { return stream.str(); }
};    

class MyClass
{
public:
    MyClass(const string &s) : MyString(s) {}
    string MyString;
};

int main()
{
    MyClass myClass(Streamer() << "something" << "world");
    cout << myClass.MyString;
}

Answer 4

redesign your solution. if your c-tor needed string it should accept string.
also in this and similar cases will better if your constructor will accept const reference.

no matching function for call to ‘MyClass(std::basic_ostream <..>&)

error happened because operator<< defined for and returns std::basic_ostream not std::stringstream object. ofcourse you could use

dynamic_cast< const std::stringstream& >( s << "hello" << "world" )

but your team lead could fire you for this code:)

BTW:

MyClass mc = MyClass("Some string" << anotherString);

could be rewriten as

MyClass mc("Some string" << anotherString);