The strtoumax function converts a string of ASCII characters pointed
    to by nptr to the appropriate unsigned numeric values. strtoumax is a
    synonym for strtoull

    The function recognizes strings in various formats, depending on the
    value of the base. Any leading white-space characters (as defined by
    isspace in <ctype.h>) in the given string are ignored.

    The function recognizes an optional plus or minus sign, then a
    sequence of digits or letters that may represent an integer constant
    according to the value of the base. The first unrecognized character
    ends the conversion and is pointed to by endptr.

    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.