passing nullptr to std::stoi

Question

For the stoi function documented in the below reference,

http://www.cplusplus.com/reference/string/stoi/

int stoi (const string&  str, size_t* idx = 0, int base = 10);

It is then used as

int i_hex = std::stoi (str_hex,nullptr,16);

Here the idx is not defined as constant pointer (size_t * const idx =0), why can we pass nullptr as the arguments? Isn't nullptr a constant?

Answer 1

nullptr is not a pointer at all . It is a prvalue of type std::nullptr_t . But, it can be implicitly converted to any pointer type. Whether the pointer type is const, volatile, etc does not matter. So, the above code is fine.