Storing objects in Vector.

This is a discussion on Storing objects in Vector. within the C++ Programming forums, part of the General Programming Boards category; How would i go about storing an arbitrary number of objects within a vector. If say I have 20 created ...

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    Storing objects in Vector.

    How would i go about storing an arbitrary number of objects within a vector.

    If say I have 20 created objects, how could I loop through them and 'push_back' to the vector without manually doing each one?

    Also, whilst I am coding I can create objects easily, is there a way that the person using the program can create objects, such as adding a book to a library?

    I don't yet know about pointers, so please no advice yet on that (it will probably just confuse me more)

    Thanks,

    Darren.

    NB....this isn't homework. Currently working on chapter 9 of Stroustrup PPP.

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    C++ Witch laserlight's Avatar
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    Well, given a vector<T> named v, you might write:
    Code:
    v.push_back(T(1, args));
    v.push_back(T(2, args));
    // etc
    v.push_back(T(20, args));
    and thus populate the vector with those 20 objects. If they are all (initially) the same as you create the vector, you could just write:
    Code:
    vector<T> v(20, T(whatever, args));
    As for your users creating objects: when your user performs some action to add a book to the library, your program then correspondingly uses push_back on the vector. The user himself/herself should be thinking "adding a book to the library", not "adding a book object to a vector".
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    Quote Originally Posted by laserlight View Post
    Well, given a vector<T> named v, you might write:
    Code:
    v.push_back(T(1, args));
    v.push_back(T(2, args));
    // etc
    v.push_back(T(20, args));
    and thus populate the vector with those 20 objects. If they are all (initially) the same as you create the vector, you could just write:
    Code:
    vector<T> v(20, T(whatever, args));
    As for your users creating objects: when your user performs some action to add a book to the library, your program then correspondingly uses push_back on the vector. The user himself/herself should be thinking "adding a book to the library", not "adding a book object to a vector".
    Thanks for the response. I am fairly new to C++ and not totally sure what you mean by args, if you could please elaborate.

    Also, the problem I am having with user creating objects, is how to give the created object a name? How do you set that initial object name?

    Thanks,

    Darren.

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    C++ Witch laserlight's Avatar
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    Quote Originally Posted by darren78
    Thanks for the response. I am fairly new to C++ and not totally sure what you mean by args, if you could please elaborate.
    Whatever arguments you need to invoke the constructor.

    Quote Originally Posted by darren78
    Also, the problem I am having with user creating objects, is how to give the created object a name? How do you set that initial object name?
    If the object is supposed to have a name, make the name a member variable, e.g., a book has a title.
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    Quote Originally Posted by laserlight View Post
    Whatever arguments you need to invoke the constructor.


    If the object is supposed to have a name, make the name a member variable, e.g., a book has a title.
    Thanks again. It's making a little more sense now. From my readings so far, I was under the impression that when creating objects they had to be given a name.

    If I create an object without a name, how do I access the data relating to a specific object?

    Looking at the book so far, I have accessed them by using the notation object.member.

    Thanks.

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    C++ Witch laserlight's Avatar
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    Quote Originally Posted by darren78
    If I create an object without a name, how do I access the data relating to a specific object?
    In the case of a vector, you could refer to the object by index. Perhaps you could search for the object in the vector by name, id, etc. Or perhaps instead of using a vector, you use a map, mapping the name, id, or some other key to the object.
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    Thanks. I understand now.

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    If you intend on removing books and need to access the books later based on an ID or a key then a map is the best choice. Vector is great until you realize that when you remove an object it invalidates all iterators beyond the point of removal. This means that if you are using the index in the vector as the book ID the moment you remove all of the stored IDs for books that lie beyond the point of removal those IDs are all incorrect. You can remedy this via a listener/observer pattern but the best choice is to use the right container for the job.

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    Quote Originally Posted by Bubba View Post
    If you intend on removing books and need to access the books later based on an ID or a key then a map is the best choice. Vector is great until you realize that when you remove an object it invalidates all iterators beyond the point of removal. This means that if you are using the index in the vector as the book ID the moment you remove all of the stored IDs for books that lie beyond the point of removal those IDs are all incorrect. You can remedy this via a listener/observer pattern but the best choice is to use the right container for the job.
    Thanks Bubba. I will take a look at maps. The reason I have chosen vectors is that I am currently working through a book that has not yet reached maps, but I will take a look at them for this task.

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