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What is a container? As I understand it:

  • An abstract data type is merely a logical description of the way the data will be stored and the operations that will be permitted on that data. For example, a stack is defined as a data type with the operations push, pop, etc. and LIFO access.

  • A data structure is the actual implementation of this abstract definition, in some computer programming language, for example, a stack in C++ is implemented in the standard library, as std::stack.

Firstly, please correct/enhance my current understanding of the aforementioned distinction.

Secondly, what exactly is a container? I hear this word thrown around quite often. Is it the same as my definition of a data structure?

Also, wikipedia has three separate entries for these terms.

Emil Laine
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ordinary
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    it's all about context. I don't think it make any sense to discuss them separately as two bare words. – xvatar Jun 27 '12 at 01:40
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    Agreed. If you're in the context of a given programming language or implementation then these words can have very explicit meanings, but outside of that context they're pretty ambiguous. Except ADT, which always means what is stated above. – Johansensen Jun 27 '12 at 01:55

4 Answers4

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Nothing, really. They're just two words for the same term, as we humans love to do. However, afaik, the official CS term is data structure, and the C++ Standard has specific C++ requirements for Container. However, in general, they are equivalent.

Puppy
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You're correct in your impressions of ADT vs data structure- although they're interchangeable to a fairly great extent. An ADT is explicitly abstract, a data structure is a more general term that can be totally abstract, or refer to implementation details as well.

A container is a very abstract idea, but generally it implies (to me anyway) some form of encapsulation- in the sense that it might mask complexities of an underlying object, or possibly present a uniform interface to a range of different possible underlying objects. It's a word so firmly rooted in the programmer vocabulary that people use it all the time, and as such its meaning is very blurry. ;)

Johansensen
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  • However, it seems that (at least in the C++ world with which I'm not hugely familiar) the term `container` is sometimes used synonymously with `collection`. – Johansensen Jun 27 '12 at 01:37
  • A `collection` is a type of ADT- one which contains a variable number of items, usually of a uniform type. Different collection types can be associative (e.g. hashmaps), ordered (e.g. lists), etc. – Johansensen Jun 27 '12 at 01:38
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A Container is a subset of data structures. C++ imposes special requirements on containers, which are implementations of different data structures.

A data structure is, per wikipedia: "a particular way of storing and organizing data". A container is a C++ construct that is a collection of records, which is itself a data structure.

Robert Mason
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As said by other, those terms are so widely used that they are used with various meanings, but here are the usages I have most often encountered.

Data structure is a term from computer science, it can be used in a theoratical discussion without reference to any specific language. There are many data structures discussed in books about algorithms, like queues, trees, hashtables... A data structure can be implemented in virtually any language.

Container is a term rather used in the contect of a specific language, when there is an available library of already implemented containers that the programmer can use right away. Several disctinct libraries can implement the same (abstract) data structure (for instance, a simply linked list), but with distinct containers, i.e. distinct source code and distinct names (one could be called "queue", another one "fifo", and a third one "stack").

Furthermore, a container must be a way to store other types, e.g. vector stores ints. As an example, there are several ways to represent a graph in memory: adjacency matrix, adjacency lists, forward-star... All of these are data structures, but they are not containers, as they do not contain other types, they just represent the nodes and links of the graph. The data stored by these data structures are the nodes and links.

jrouquie
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