std::strings's capacity(), reserve() & resize() functions

Question

I wan to use std::string simply to create a dynamic buffer and than iterate through it using an index. Is resize() the only function to actually allocate the buffer?

Answer 1

The capacity is the length of the actual buffer, but that buffer is private to the string; in other words, it is not yours to access. The std::string of the standard library may allocate more memory than is required to storing the actual characters of the string. The capacity is the total allocated length. However, accessing characters outside s.begin() and s.end() is still illegal.

You call reserve in cases when you anticipate resizing of the string to avoid unnecessary re-allocations. For example, if you are planning to concatenate ten 20-character strings in a loop, it may make sense to reserve 201 characters (an extra one is for the zero terminator) for your string, rather than expanding it several times from its default size.