I wanted to know how I can parse an IPv6 address in C and convert it to a 128 bit value?
So a hex address like 1:22:333:aaaa:b:c:d:e
needs to be convert
You can use getaddrinfo() POSIX function. It is more flexible than inet_pton()
, for example it automatically detects IPv4 and IPv6 address formats, it can resolve even hostnames (using DNS resolving) and port/service names (using /etc/services
).
#include <sys/types.h>
#include <netdb.h>
#include <netdb.h>
....
const char *ip6str = "::2";
struct sockaddr_storage result;
socklen_t result_len;
struct addrinfo *res = NULL;
struct addrinfo hints;
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = PF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_DEFAULT | AI_NUMERICHOST | AI_NUMERICSERV;
rc = getaddrinfo(ip6str, NULL, &hints, &res);
if (rc != 0)
{
fprintf(stderr, "Failure to parse host '%s': %s (%d)", ip6str, gai_strerror(rc), rc);
return -1;
}
if (res == NULL)
{
// Failure to resolve 'ip6str'
fprintf(stderr, "No host found for '%s'", ip6str);
return -1;
}
// We use the first returned entry
result_len = res->ai_addrlen;
memcpy(&result, res->ai_addr, res->ai_addrlen);
freeaddrinfo(res);
The IPv6 address is stored in the struct sockaddr_storage result
variable.
if (result.ss_family == AF_INET6) // Ensure that we deal with IPv6
{
struct sockaddr_in6 * sa6 = (struct sockaddr_in6 *) &result;
struct in6_addr * in6 = &sa6->sin6_addr;
in6->s6_addr[0]; // This is a first byte of the IPv6
in6->s6_addr[15]; // This is a last byte of the IPv6
}
if you can use boost, something like this should work:
#include<boost/asio.hpp>
using boost::asio::ip;
bool parseIpv6String(std::string ipv6_string, char* dest){
try{
address_v6 addr = address_v6::from_string(ipv6_string);
memcpy(dest,addr.to_bytes().data(), 16);
}catch(...){
return false;
}
return true;
}
It is a bit more portable than for example POSIX specific functions.
To parse IPv6 in C, you need to build yourself a utility function, which tokenized string (colon for hex blocks, and forward-slash for subnet bits).
In Windows, you can use WSAStringToAddress, which is available since Windows 2000.
You can use POSIX inet_pton to convert a string to a struct in6_addr
.
#include <arpa/inet.h>
...
const char *ip6str = "::2";
struct in6_addr result;
if (inet_pton(AF_INET6, ip6str, &result) == 1) // success!
{
//successfully parsed string into "result"
}
else
{
//failed, perhaps not a valid representation of IPv6?
}
Rosetta has samples in several languages: https://rosettacode.org/wiki/Parse_an_IP_Address