size_type capacity() const noexcept;
Returns: The total number of elements that the vector can hold without requiring reallocation.
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.
Remarks: Reallocation invalidates all the references, pointers, and iterators referring to the elements in the sequence. It is guaranteed that no reallocation takes 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().
Remarks: 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 ]
Effects: Exchanges the contents and capacity() of *this with that of x.
Complexity: Constant time.
Effects: If sz <= size(), equivalent to erase(begin() + sz, end());. If size() < sz, appends sz - size() value-initialized elements to the sequence.
Requires: T shall be CopyInsertable into *this.
void resize(size_type sz, const T& c);
Effects:
if (sz > size())
insert(end(), sz-size(), c);
else if (sz < size())
erase(begin()+sz, end());
else
; // do nothing
Requires: If an exception is thrown other than by the move constructor of a non-CopyInsertable T there are no effects.
reserve() uses Allocator::allocate() which may throw an appropriate exception.