26 Containers library [containers]

26.3 Sequence containers [sequences]

26.3.11 Class template vector [vector]

26.3.11.3 vector capacity [vector.capacity]

size_type capacity() const noexcept;
Returns: The total number of elements that the vector can hold without requiring reallocation.
void reserve(size_type n);
Requires: T shall be MoveInsertable into *this.
Effects: A directive that informs a vector of a planned change in size, so that it can manage the storage allocation accordingly.
After reserve(), capacity() is greater or equal to the argument of reserve if reallocation happens; and equal to the previous value of capacity() otherwise.
Reallocation happens at this point if and only if the current capacity is less than the argument of reserve().
If an exception is thrown other than by the move constructor of a non-CopyInsertable type, there are no effects.
Complexity: It does not change the size of the sequence and takes at most linear time in the size of the sequence.
Throws: length_­error if n > max_­size().261
Remarks: Reallocation invalidates all the references, pointers, and iterators referring to the elements in the sequence.
No reallocation shall take place during insertions that happen after a call to reserve() until the time when an insertion would make the size of the vector greater than the value of capacity().
void shrink_to_fit();
Requires: T shall be MoveInsertable into *this.
Effects: shrink_­to_­fit is a non-binding request to reduce capacity() to size().
[Note
:
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.
If an exception is thrown other than by the move constructor of a non-CopyInsertable T there are no effects.
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 swap(vector& x) noexcept(allocator_traits<Allocator>::propagate_on_container_swap::value || allocator_traits<Allocator>::is_always_equal::value);
Effects: Exchanges the contents and capacity() of *this with that of x.
Complexity: Constant time.
void resize(size_type sz);
Effects: If sz < size(), erases the last size() - sz elements from the sequence.
Otherwise, appends sz - size() default-inserted elements to the sequence.
Requires: T shall be MoveInsertable and DefaultInsertable into *this.
Remarks: If an exception is thrown other than by the move constructor of a non-CopyInsertable T there are no effects.
void resize(size_type sz, const T& c);
Effects: If sz < size(), erases the last size() - sz elements from the sequence.
Otherwise, appends sz - size() copies of c to the sequence.
Requires: T shall be CopyInsertable into *this.
Remarks: If an exception is thrown there are no effects.
reserve() uses Allocator​::​allocate() which may throw an appropriate exception.