[Boost-users] Re: Library array

Hi Dave,

Vector is more flexible than array. But this flexibility comes at a cost. Even if you reserve space for a known number of elements, vector cannot assume that you won't add or remove elements. So there's a minor overhead in keeping track of when it needs to expand if you choose to add more elements.

Also, reserving elements for a vector only guarantees that space for _at least_ that number of elements is reserved (see 23.2.4.2 in the standard) - it may in fact reserve more in the hope that it won't need to reallocate in the event you choose to add more elements. So it may consume more memory.

Boost::array can avoid all of those potential issues because you specify the number of elements at compile-time and it cannot change.

But the main reason to use boost::arrays IMHO is for clarity. If you know how many elements are required they let you express that clearly - something that neither vector nor standard arrays can do. This is of particular advantage when you consider passing a container with n elements to a function:

void thisFunctionRequiresA10ElementArray(const boost::array tenElements); void notSureHowManyElementsThisNeeds(const std::vector<T> elements);

Hope that helps!

Cheers, Matt

PS Glad to provide you with a nice $100 bill... ;)

Hmmm, I suppose my first question leads naturally to another... Why would one prefer a tuple to a simple struct?