Have a C++ Class act like a custom ostream, sstream

Question

I have a C++ class MyObject and I want to be able to feed this data like I would to a osstream (but unlike a direct sstream, have the incoming data be formatted a special way). I can't seem to figure out how to overload a operator for MyObject to eat input given to it.

class MyObject { public: ostringstream s; FEEDME }; int main() { MyObject obj; obj.FEEDME << "Hello" << 12345; // I want obj.s == ":Hello::12345:" }

I want it so every item fed in be surrounded by : :

So in the given example, s = ":Hello::12345" should be the final outcome. What my question is, how can I tell the object that when ever a <<something, put : : around the something.

Is this possible?

Evan Teran · Accepted Answer · 2009-05-05 02:16:51Z

10

try this:

class MyObject { public: template <class T> MyObject &operator<<(const T &x) { s << ':' << x << ':'; return *this; } std::string to_string() const { return s.str(); } private: std::ostringstream s; }; MyObject obj; obj << "Hello" << 12345; std::cout << obj.to_string() << std::endl;

There are certain things you won't be able to shove into the stream, but it should work for all the basics.

answered May 5, 2009 at 2:16

Evan Teran

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3 Comments

The Unknown Over a year ago

Thanks, I think I have footing on how to implement it now, still getting a error "error: invalid use of member (did you forget the ‘&’ ?)" for MyObject &operator<<(const T &x) { But will mess with it and get resolved. Thank you good sir.

Evan Teran Over a year ago

I think that compiles fine in g++ 4.3.3, what compiler are using?

The Unknown Over a year ago

g++ (GCC) 4.3.2, you are correct it compiles and works exactly like I want it to! Thank you. The problem seems to be something particular to my program.

Community · Accepted Answer · 2017-05-23 12:13:35Z

1

You may find the answers for How do I create my own ostream/streambuf? helpful.

edited May 23, 2017 at 12:13

CommunityBot

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answered May 5, 2009 at 2:15

bdonlan

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Comments

Loki Astari · Accepted Answer · 2009-05-05 04:38:17Z

I would take a slightly different approach and create a formater object.
The formater object would then handle the inserting of format character when it is applied to a stream.

#include <iostream> template<typename T> class Format { public: Format(T const& d):m_data(d) {} private: template<typename Y> friend std::ostream& operator<<(std::ostream& str,Format<Y> const& data); T const& m_data; }; template<typename T> Format<T> make_Format(T const& data) {return Format<T>(data);} template<typename T> std::ostream& operator<<(std::ostream& str,Format<T> const& data) { str << ":" << data.m_data << ":"; } int main() { std::cout << make_Format("Hello") << make_Format(123); }

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