[Newbie] C++ call by reference question

This is a discussion on [Newbie] C++ call by reference question within the C++ Programming forums, part of the General Programming Boards category; Hello! I have typedefs like the following: Code: typedef std::set<std::string>TBookKey; typedef std::vector<bookObjs>TBookValues; typedef std::map<bookKey, bookValues> TBookMap; And, member variable declaration: ...

  1. #1
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    Lightbulb [Newbie] C++ call by reference question

    Hello!

    I have typedefs like the following:
    Code:
    typedef std::set<std::string>TBookKey;
    typedef std::vector<bookObjs>TBookValues;
    typedef std::map<bookKey, bookValues> TBookMap;
    And, member variable declaration:
    Code:
    private:
    TBookMap bookMap;
    ** Question **
    Is it possible to create an API to obtain:
    The pointer or reference to the TBookKey (set), and TBookValues (vector) of the a specific pair from the bookMap? (Not a copy of them)

    I think, if I define the API signature such as:
    Code:
    // iterate through BookMap to get the actual Key/Value reference of specified pair.
    
    void
    GetBookMapPair(const int bookID, TBookKey& key, TBookValues& value);
    
    The caller will always get a copy of TBookKey and TBookValues of the specified (bookID) pair, but not the pointer/reference of the Key/Value. Because that the operator= of set/vector is overloaded to make a copy. Is it correct? Any suggestions/comments?

    may tks!

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    No, you're not correct.

    The function GetBookMapPair() accepts two argum,ents (key and value) by reference. Those arguments are not copied.
    Right 98% of the time, and don't care about the other 3%.

  3. #3
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by grumpy View Post
    No, you're not correct.

    The function GetBookMapPair() accepts two argum,ents (key and value) by reference. Those arguments are not copied.
    I *think* what he's asking about is to get a reference to the actual object in the set or vector, given the ID number of ... I'm not sure what. (In other words, can you force a set or a vector to give you a reference to an object that it contains, rather than a copy of it?)

    On the other hand, I'm not sure why we have a map from a set of strings to a vector of bookObjs in the first place, so there is quite a mystery.

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    Quote Originally Posted by tabstop View Post
    I *think* what he's asking about is to get a reference to the actual object in the set or vector
    Maybe. In that case, yes it is possible. A function can return a reference. Some of the member functions of set and vector (including incantations of operator[]) do so.
    Right 98% of the time, and don't care about the other 3%.

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