std::vector::capacity
From cppreference.com
                    
                                        
                    
                    
                                                            
                    
| size_type capacity() const; | ||
Returns the number of elements that the container has currently allocated space for.
| Contents | 
[edit] Parameters
(none)
[edit] Return value
Capacity of the currently allocated storage.
[edit] Exceptions
| (none) | (until C++11) | 
| 
noexcept specification:   noexcept | (since C++11) | 
[edit] Complexity
Constant.
[edit] See also
| returns the number of elements (public member function) | |
| reserves storage (public member function) |