CODEWITHSUNDEEP
c++stlstdlist
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Reputation: 21817

std::list fixed size

How can I create std::list with a fixed element count?

Upvotes: 5

Views: 16932

Answers (4)

Steve Townsend
Steve Townsend

Reputation: 54138

#include <list>

// list with 5 elements, using default constructor
const size_t fixedListSize(5);
std::list<int> mylist(fixedListSize);

If you want it to always have exactly 5 elements you'd have to wrap it in a facade class to prevent insertion and erasure.

If that is indeed what you want, you'd be better off using a different container instead of list, since as noted in other responses you would be hiding the most advantageous features of list.

Upvotes: 10

CashCow
CashCow

Reputation: 31435

I would have to ask you, why you want it to have a fixed number of elements and why use a list?

It could be that the user is implementing a cache with a limited number of elements and an LRU policy of removal. In that case a list is a good collection to use. Any time an element is accessed, you splice that element to the front of the list. If you need to insert a new elemenet (so the list gets full) you pop off the back of the list.

You can also maintain some kind of lookup for the elements but std::list is the best class to handle LRU.

Upvotes: 2

sth
sth

Reputation: 229583

If you just want a fixed size container, maybe you are looking for std::tr1::array. (Or just std::array for C++0x.)

If you don't insert or remove elements I don't think there is any advantage in using std::list instead of std::array or std::vector.

Upvotes: 14

Keynslug
Keynslug

Reputation: 2766

You should use std::list constructor.

explicit list (size_type n, const T& value = T(), const Allocator& = Allocator());

Just specify at time of creation exact count of elements.

std::list<int> someList(20);

You could specify initial value for each element too.

std::list<int> someList(20, int(42));

std::list::resize is the right solution too.

Upvotes: 3

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