array<int,4> a1 = {1,2,3,4};
array<int,4>::iterator itr1 = a1.begin(); //Ok
array<int>::iterator itr2 = a1.begin(); //Compiler error. why not allowed?
//Iteration
while(itr1 != a1.end())
{
cout<<"\n "<<*itr1;
itr1++;
}
since we always iterate from begin() to end() Is there any special reason for mentioning size in array iterator template?
When you use a template with different template arguments the generated classes are not in any sense the same. So std::array<int, 1> and std::array<int, 2 are not the same type. When you instantiate the template a specialised copy of the class is created thus the above example creates two distinct specialisations of std::array one with the arguments <int, 1> and one with <int, 2>. Even though the specialisations have very similar implementation they are not the same. As a consequence of this std::array<int, 1>::iterator is not the same type as std::array<int, 2>::iterator. They are two different specialisations.
Your attempt with std::array<int>, which seems pretty logical at first glance, is not correct because std::array expects two template arguments and not one. The auto keyword was introduced in part to make these kinds of things easier, use it.
PS: Thanks to aaronman for clarifying the answer.
iterator type is implementation defined, as this comment seemed to suggest otherwise, and the edited answer makes claims about the implementation. It is subtle detail, but I wanted accentuate the difference, as I have seen it be the source of a problem in code.std::array is a compile time fixed size container which has its advantages. (For a run time dynamic container you can use std::vector) The size must be set at compile time so, array<int> is illegal and even doesn't exists as a type.
This type is a good alternative for traditional arrays such as int a[123]. You can pass std::array to functions easier than traditional arrays and whenever you're using std::array you know the length.
Functions .begin() and .end() make it consistence to other containers and you can iterate over it like other STL types. It's important to know array<int, 10> and array<int, 11> are two different types with same interfaces.
array<int>to bestd::arraytakes two template params