#define SILC_STR_UI8_STRING() ...
    #define SILC_STR_UI8_STRING_ALLOC() ...
    #define SILC_STR_UI16_STRING() ...
    #define SILC_STR_UI16_STRING_ALLOC() ...
    #define SILC_STR_UI32_STRING() ...
    #define SILC_STR_UI32_STRING_ALLOC() ...

    Unsigned NULL terminated string. Note that the string must be
    NULL terminated because strlen() will be used to get the length of
    the string.

    Formatting:    SILC_STR_UI32_STRING(unsigned char *)
    Unformatting:  SILC_STR_UI32_STRING(unsigned char **)

    Unformatting procedure will check for length of the string from the
    buffer before trying to get the string out. Thus, one *must* format the
    length as UI_INT or UI_SHORT into the buffer *before* formatting the
    actual string to the buffer, and, in unformatting one must ignore the
    length of the string because unformatting procedure will take it
    automatically.

    Example:

    Formatting:    ..., SILC_STR_UI_INT(strlen(string)),
                        SILC_STR_UI32_STRING(string), ...
    Unformatting:  ..., SILC_STR_UI32_STRING(&string), ...

    I.e., you can ignore the formatted length field in unformatting.

    UI8, UI16 and UI32 means that the length is considered to be
    either char (8 bits), short (16 bits) or int (32 bits) in
    unformatting.

    _ALLOC routines automatically allocates memory for the variable sent
    as argument in unformatting.