Question

What does the below syntax represents?

typedef UserArray<T,W,L,H> MyType;

where:

• T = type of an array element
• W = width of an array element, 0 < W < 8
• L = low bound of array index (preferably zero)
• H = high bound of array index

Can anyone explain me using example for above declaration?

Does this concepts comes under STL?

Answer 1

UserArray is a class template that takes four template parameters.

It’s probably defined like that:

template<class T, int W, int L, int H> // parameter names might differ
class UserArray
{
    // ...
};

typedef is used to define aliases for types. This:

typedef UserArray<T,W,L,H> MyType;

Defines an alias for UserArray using the specified template parameters. T must be a type, and W, L and H must be compile-time integer constants. The resulting alias is called MyType, and using it is like using UserArray with the same parameters.

Those techniques are used to simplify typing when a type is used a lot in many places. For instance, you can do this:

typedef std::vector<int> IntVector;

IntVector vect; // a vector of ints