I developing a network application and using socket APIs.
I want to set sin6_addr byte order of sockaddr_in6 structure.
For 16 bits or 32 bits variables, it is simple: Using htons or htonl:
// IPv4
sockaddr_in addr;
addr.sin_port = htons(123);
addr.sin_addr.s_addr = htonl(123456);
But for 128 bits variables, I dont know how to set byte order to network byte order:
// IPv6
sockaddr_in6 addr;
addr.sin6_port = htons(123);
addr.sin6_addr.s6_addr = ??? // 16 bytes with network byte order but how to set?
Some answers may be using htons for 8 times (2 * 8 = 16 bytes), or using htonl for 4 times (4 * 4 = 16 bytes), but I don't know which way is correct.
Thanks.
The s6_addr
member of struct in6_addr
is defined as:
uint8_t s6_addr[16];
Since it is an array of uint8_t
, rather than being a single 128-bit integer type, the issue of endianness does not arise: you simply copy from your source uint8_t [16]
array to the destination. For example, to copy in the address 2001:888:0:2:0:0:0:2
you would use:
static const uint8_t myaddr[16] = { 0x20, 0x01, 0x08, 0x88, 0x00, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02 };
memcpy(addr.sin6_addr.s6_addr, myaddr, sizeof myaddr);