CODEWITHSUNDEEP
c++stringstringstream
Nick Bolton
Nick Bolton

Reputation: 39550

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

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) { /* ... */ }

Upvotes: 2

Views: 484

Answers (4)

Eclipse
Eclipse

Reputation: 45493

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;
}

Upvotes: 1

bayda
bayda

Reputation: 13581

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);

Upvotes: 4

David Norman
David Norman

Reputation: 19879

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.

Upvotes: 1

David Norman
David Norman

Reputation: 19879

Your compile error looks like have included 

<iosfwd>

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

<sstream>

in the cxx file.

Upvotes: 2

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