nptr

    A pointer to the wide-character string to be converted to an
    unsigned long.

 endptr

    The address of an object where the function can store the address
    of the first unrecognized character encountered in the conversion
    process (the character that follows the last character in the
    string being converted). If endptr is a NULL pointer, the address
    of the first unrecognized character is not retained.

 base

    The value, 2 through 36, to use as the base for the conversion.

    If base is 16, leading zeros after the optional sign are ignored,
    and 0x or 0X is ignored.

    If base is 0, the sequence of characters is interpreted by
    the same rules used to interpret an integer constant: after
    the optional sign, a leading 0 indicates octal conversion, a
    leading 0x or 0X indicates hexadecimal conversion, and any other
    combination of leading characters indicates decimal conversion.