Re: Require Help in Parsing strings!!!
- From: Ben C <spamspam@xxxxxxxxx>
- Date: 27 Mar 2006 06:59:44 GMT
On 2006-03-27, None <vedanarayanan.ganesan@xxxxxxxxx> wrote:
You can use the power of union and combinate with struct to disect the
stream of bytes into organized data of your class. For eg your struct
[...]
typedef struct __ns_rr {
char name[NS_MAXDNAME];
uint16_t type;
uint16_t rr_class;
uint32_t ttl;
uint16_t rdlength;
union
{
const uchar_t rdata[MAX_BYTES_POSSBL_IN_ANY_DATA];
struct NAPTR
{
unsigned int order;
unsigned int preference;
char flags[SOME_SIZE1];
char services[SOME_SIZE2];
char regexp[SOME_SIZE3];
char replacement[SOME_SIZE4];
};
struct Another_NAPTR
{
};
} any_one_data;
and so on...
} ns_rr;
Use the 'type' field of '__ns_rr' to determine which field of the union
(that is any_one_data) has to accessed.
I think this is best way of organizing a stream of bytes and
interpreting it based on some type.
[...]
Not sure exactly what this is for, but if it involves writing a stream
of bytes into rdata and then reading it out of one of struct NAPTR etc.
(don't they need names anyway?) don't forget about structure padding--
you can't make any assumptions about how the bytes in rdata and the data
in the structs match up apart from for the first member of each struct.
See http://www.c-faq.com/struct/io.html and
http://www.c-faq.com/struct/padding.html.
Also, better style not to start identifiers with underscores (these are
"reserved").
In general though unions like this are a good way of reinterpreting data
where that's necessary.
.
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