Bitshift operator overloading help (weird)

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  1. #1
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    Bitshift operator overloading help (weird)

    Hey,

    I'm working on a Solaris box and trying to overload the left bitshift operator as a "print" function in an object I have, so I can do:
    Code:
    std::cout << obj_name << std::endl;
    Every possible example I can find has 2 arguments, LHS, RHS. The prototype for this system appears to only have one, the RHS.

    If I add a second argument to the overloaded definition, I get:
    Code:
    file_name.h:53: error: `std::ostream& class_name::operator<<(std::ostream&, const class_name&)' must take exactly one argument
    I put a printf inside the overloaded operator and put:
    Code:
    obj << std::cout;
    And it prints the hardcoded string literal in the operator overloading..

    Does this mean I can only overload the RHS, or am I doing it wrong..

    I mean I think I could do it like:
    Code:
    std::cout << obj << std::cout
    Because it returns an ostream reference..


    Additional Notes:
    I didn't friend the overload, it's in the header in the class declaration.

  2. #2
    C++ Witch laserlight's Avatar
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    Overload as a non-member function.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Quote Originally Posted by laserlight View Post
    Overload as a non-member function.
    Hey,

    That works, one thing, though.

    I'm trying to put it in a header file (it just calls another function, it's a one liner), but then I geta linker error for multiple def, compiles fine if I put it in the cpp..but I'd hate to have a cpp just for one one line function. It's within the class sentry.

    Any way I can do that?

    NVM: I'm going to scrap the idea.

    Sorry about that, but I'm sure I would have asked the question eventually. Why did I scrap?

    Well when calling...
    Code:
    std::cout << *obj_name << std::endl;
    Looks a hell of a lot worse than:
    Code:
    obj_name->Display();
    Last edited by Syndacate; 01-12-2011 at 01:40 PM.

  4. #4
    Registered User NeonBlack's Avatar
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    Quote Originally Posted by Syndacate View Post
    Hey,
    Sorry about that, but I'm sure I would have asked the question eventually. Why did I scrap?

    Well when calling...
    Code:
    std::cout << *obj_name << std::endl;
    Looks a hell of a lot worse than:
    Code:
    obj_name->Display();
    I would keep it. While your Display() function serves the single purpose of printing to std::cout, you can also use operator<< with other types of streams, such as file streams and stringstreams.
    I copied it from the last program in which I passed a parameter, which would have been pre-1989 I guess. - esbo

  5. #5
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by Syndacate
    I'm trying to put it in a header file (it just calls another function, it's a one liner), but then I geta linker error for multiple def, compiles fine if I put it in the cpp..but I'd hate to have a cpp just for one one line function. It's within the class sentry.
    Declare the function to be inline, e.g.,
    Code:
    inline std::ostream& operator<<(std::ostream& out, const X& x)
    {
        return x.Display(out);
    }
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Quote Originally Posted by NeonBlack View Post
    I would keep it. While your Display() function serves the single purpose of printing to std::cout, you can also use operator<< with other types of streams, such as file streams and stringstreams.
    If it was my own project, I'd say sure, but it's for a school project. It wasn't required to overload the operator, they didn't get even get to it yet - just figured it'd be convenient to just cout the puzzle, like how everything in java has a toString(), you can just cout the object...then I implemented it, and it didn't look as nice as just ptr->Display();. You know?

    Quote Originally Posted by laserlight View Post
    Declare the function to be inline, e.g.,
    Code:
    inline std::ostream& operator<<(std::ostream& out, const X& x)
    {
        return x.Display(out);
    }
    Ah, yeah, thanks. Not sure why I didn't think of that, it was inline when it was a member function...start to not think right after coding too long...lol.

  7. #7
    Chi! whiteflags's Avatar
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    Quote Originally Posted by NeonBlack View Post
    I would keep it. While your Display() function serves the single purpose of printing to std::cout, you can also use operator<< with other types of streams, such as file streams and stringstreams.
    Well if you weren't going to use operator overloading, I think a Display function could be modified to work with an ostream argument, which gives you all the polymorphism you need to work with other types of streams.

    operator>> and operator<< are only a convention -- a very widely appreciated convention, but you could easily implement both to please everyone.

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