Size versus Capacity

The number of elements a string has (str.size()) is in general smaller than the number of elements for which space is reserved: str.capacity(). Therefore if we add elements to a string, new memory will not necessarily be allocated. std:max_size() return the maximum amount of elements a string can have. For the three methods the following relation holds: str.size() <= str.capacity() <= str.max_size().

The following table shows the methods for dealing with memory management of strings.

Methods	Description
str.empty()	Checks if str has elements.
str.size(), str.length()	Number of elements of the str.
str.capacity()	Number of elements str can have without reallocation.
str.max_size()	Number of elements str can maximal have.
str.resize(n)	Increases str to n elements.
str.reserve(n)	Reserves memory for a least n elements.
str.shrink_to_fit()	Adjusts the capacity of the string to it’s size.

The request str.shrink_to_fit() is, as in the case of std::vector, non-binding.