Dynamic array of objects in C++

Question

I'm trying to create a dynamic array of objects, similar to ArrayLists in Java. I'm new at C++ and can't get it to work.

class Album{

private:

public:
    void addPhoto(Photo p){

    }

};

What should my private datamember look like and how do I add p to it? And do I need a pointer for some reason?

You should look into the STL; there are a variety of container types in there (`vector` is the one that comes to mind here, but there may be others that suit your problem better). — James Aylett, Mar 11 '12 at 23:40
you may want to pay attention to heap space allocation. if the Album object is going to be big, maybe it is better to allocate with new. — , Mar 12 '12 at 18:16

score 2 · Answer 1 · answered Mar 11 '12 at 23:43

2

You should use an std::vector.

answered Mar 11 '12 at 23:43

mfontanini

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score 2 · Accepted Answer · edited Mar 12 '12 at 01:39

2

The functionality you look for already exits in the stl collection classes and and with out knowing you application it would be had to tell you weather you needed a pointer or not.

The basic layout of you underlying container could be something like this.

class Album{    

public:
    void addPhoto(Photo p){
         Photos.push_back(p); 
    }
private:
    std::vector<Photo> Photos; 

};

edited Mar 12 '12 at 01:39

answered Mar 11 '12 at 23:44

rerun

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Just curious, where did you originally learn to put an underscore for class members (i.e. `_Photos`), I know doing it after like (`Photos_`) is popular too which I believe was popularized by "C++ Coding Standards" book). – Jesse Good Mar 11 '12 at 23:50
I like the answer, but you shouldn't be using `_Photo`. See this for a reasons why: http://stackoverflow.com/questions/228783/what-are-the-rules-about-using-an-underscore-in-a-c-identifier Happy to see it as Photo_ though. – Chad Mar 11 '12 at 23:53
its the current coding standard where I work just habit. I like it because of intelisense. At other jobs we have done m_ _ or absolutely no notation at all. It feels more popular in MS shops where hungarian notation dies hard. – rerun Mar 11 '12 at 23:55
Underscore-captial names are *reserved* and must not be used by user code. As such, your code exhibits *undefined behaviour*. – Kerrek SB Mar 11 '12 at 23:57
Wow did not know that at all nor have I ever run into it – rerun Mar 12 '12 at 00:01
I believe technically, `_photos` is okay but `_Photos` isn't as long as it isn't the global or std namespace. – Jesse Good Mar 12 '12 at 00:05
_Photos would not be in global namespace correct? since its a dependent identifier in a class. – rerun Mar 12 '12 at 00:10

score 0 · Answer 3 · answered Mar 11 '12 at 23:44

0

You could use the built in std::vector class that behaves very similarly to the ArrayList. (edit... looks like someone beat me to it)

answered Mar 11 '12 at 23:44

zanegray

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score 0 · Answer 4 · answered Mar 12 '12 at 00:18

@fontanini gave you a good answer, you should use vector if you need a dynamic array of objects.

But maybe you don't need a class to begin with. Not everything in C++ needs to be encapsulated in a class, unless you really need it.

Think about your data structure and what are the requirements. You might want to learn more about standard C++ library and the STL to familiarize yourself with other containers and their capabilities, limitations and objectives:

There are excellent video lectures on STL "Introduction to STL with Stephan T Lavavej"

Dynamic array of objects in C++

4 Answers4