Question

I’m looking for a way that prevents std::vectors/std::strings from growing in a given range of sizes (say I want to assume that a string will hold around 64 characters, but it can grow if needed). What’s the best way to achieve this?

Answer 1

Look at the .reserve() member function. The standard docs at the SGI site say

[4] Reserve() causes a reallocation manually. The main reason for
using reserve() is efficiency: if you know the capacity to which your
vector must eventually grow, then it is usually more efficient to
allocate that memory all at once rather than relying on the automatic
reallocation scheme. The other reason for using reserve() is so that
you can control the invalidation of iterators. [5]

[5] A vector’s iterators are invalidated when its memory is
reallocated. Additionally, inserting or deleting an element in the
middle of a vector invalidates all iterators that point to elements
following the insertion or deletion point. It follows that you can
prevent a vector’s iterators from being invalidated if you use
reserve() to preallocate as much memory as the vector will ever use,
and if all insertions and deletions are at the vector’s end.

That said, as a general rule unless you really know what is going to happen, it may be best to let the STL container deal with the allocation itself.