std::vector::capacity
From cppreference.com
                    
                                        
                    
                    
                                                            
                    
|   size_type capacity() const; 
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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)  | 
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|    reserves storage  (public member function)  |