c++ typedef generics

Question

I have this typedef in Ogre3D:

namespace Ogre {
    typedef vector<String>::type StringVector;
    ...
}

What is the "::" operator for? Does it do anything? As it is, I think this is a vector of strings - a StringVector. Correct?

`type` is some entity (obviously, a type) declared inside `vector` class. `::` operator is used to reference element `type` from `vector` namespace. — Violet Giraffe, Feb 20 '13 at 11:52
@VioletGiraffe - `vector` could be a class also (for example, if it's `std::vector`) — Kiril Kirov, Feb 20 '13 at 11:53
`::` is the scope resolution operator. If you are not familiar with this (a basic syntax element of C++), I suggest you read a [good book](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). — Angew is no longer proud of SO, Feb 20 '13 at 12:28
I am familiar with this operator, but I should have made my question more precise. I wanted to know what the construct "::type" does in the context of typedef here. — Michbeckable, Feb 20 '13 at 12:31

score 1 · Accepted Answer · answered Feb 20 '13 at 11:54

1

Defines a type StringVector which is vector<String>::type.

It seems like type is a type, defined inside vector (which is template class)

:: is called "scope resolution operator".

answered Feb 20 '13 at 11:54

Kiril Kirov

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Yes actually now I found this further definition of type: typedef std::vector< T, A > type The Vector is an STL Vector (std::vector) – Michbeckable Feb 20 '13 at 11:57
So I see, this is the way needed for a typedef from a template class. Could the identifier "type" be substituted by any identifier like "foo" etc.? – Michbeckable Feb 20 '13 at 12:06
@MichiMichbeck - if `foo` is a type, defined in the class/namespace before the scope resolution operator - then yes, `foo` can substitute `type`. – Kiril Kirov Feb 20 '13 at 12:41

score 0 · Answer 2 · answered Feb 20 '13 at 11:53

type is some entity (obviously, a type) declared inside vector class. :: operator is used to reference element type from vector namespace.

P. S. By saying "namespace" I don't only mean the actual C++ namespace feature, since classes are also similar to namespaces in that they can have nested definitions.

c++ typedef generics

2 Answers2