std::basic_string::data
From cppreference.com
                    
                                        
                    < cpp | string | basic string
                    
                                                            
                    |   const CharT* data() const;  | 
||
Returns pointer to the underlying array serving as character storage. The pointer is such that the range [data(); data() + size()) is valid and the values in it correspond to the values stored in the string.  
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 The returned array is not required to be null-terminated. If   | 
(until C++11) | 
| 
 The returned array is null-terminated, that is,  If empty() returns true, the pointer points to a single null character.  | 
(since C++11) | 
The pointer obtained from data() may be invalidated by:
- Passing a non-const reference to the string to any standard library function, or
 - Calling non-const member functions on the string, excluding operator[](), at(), front(), back(), begin(), end(), rbegin(), rend().
 
Modifying the character array accessed through data is undefined behavior.
Contents | 
[edit] Parameters
(none)
[edit] Return value
A pointer to the underlying character storage.
  data()[i] == operator[](i) for every i in [0, size()).
 | 
(until C++11) | 
  data() + i == &operator[](i) for every i in [0, size()].
 | 
(since C++11) | 
[edit] Complexity
Constant.
[edit] Exceptions
| (since C++11) | 
[edit] See also
|    (C++11)  | 
   accesses the first character  (public member function)  | 
|    (C++11)  | 
   accesses the last character  (public member function)  | 
|    returns a non-modifiable standard C character array version of the string  (public member function)  | |