long long int atoll(const char *nptr);
atoll converts the initial portion of the string pointed to by nptr to a long long int representation.
atoll does not affect the value of errno on an error. If the value of the result cannot be represented, the behavior is undefined.
Except for the behavior on error, atoll is equivalent to strtoll(nptr, (char **)NULL, 10).
atoll returns the converted value.