24 Strings library [strings]

24.3 String classes [string.classes]

24.3.2 Class template basic_­string [basic.string] Capacity [string.capacity]

size_type size() const noexcept;
Returns: A count of the number of char-like objects currently in the string.
Complexity: Constant time.
size_type length() const noexcept;
Returns: size().
size_type max_size() const noexcept;
Returns: The largest possible number of char-like objects that can be stored in a basic_­string.
Complexity: Constant time.
void resize(size_type n, charT c);
Throws: length_­error if n > max_­size().
Effects: Alters the length of the string designated by *this as follows:
  • If n <= size(), the function replaces the string designated by *this with a string of length n whose elements are a copy of the initial elements of the original string designated by *this.
  • If n > size(), the function replaces the string designated by *this with a string of length n whose first size() elements are a copy of the original string designated by *this, and whose remaining elements are all initialized to c.
void resize(size_type n);
Effects: As if by resize(n, charT()).
size_type capacity() const noexcept;
Returns: The size of the allocated storage in the string.
void reserve(size_type res_arg=0);
The member function reserve() is a directive that informs a basic_­string object of a planned change in size, so that it can manage the storage allocation accordingly.
Effects: After reserve(), capacity() is greater or equal to the argument of reserve.
Calling reserve() with a res_­arg argument less than capacity() is in effect a non-binding shrink request.
A call with res_­arg <= size() is in effect a non-binding shrink-to-fit request.
end note
Throws: length_­error if res_­arg > max_­size().231
void shrink_to_fit();
Effects: shrink_­to_­fit is a non-binding request to reduce capacity() to size().
The request is non-binding to allow latitude for implementation-specific optimizations.
end note
It does not increase capacity(), but may reduce capacity() by causing reallocation.
Complexity: Linear in the size of the sequence.
Remarks: Reallocation invalidates all the references, pointers, and iterators referring to the elements in the sequence as well as the past-the-end iterator.
If no reallocation happens, they remain valid.
void clear() noexcept;
Effects: Behaves as if the function calls:
erase(begin(), end());
[[nodiscard]] bool empty() const noexcept;
Returns: size() == 0.
reserve() uses allocator_­traits<Allocator>​::​allocate() which may throw an appropriate exception.