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I have a struct sockaddr structure containing an IPv4-mapped-IPv6 address like ::ffff:10.0.0.1. I want to obtain only the IPv4 version of it in a string (in this case, 10.0.0.1) in C programming language. How do I go about achieving it?
解决方案
As your structure contains an IPV6 address, I’ll assume your have a struct sockaddr * pointer (let’s name it addrPtr) pointing to a struct sockaddr_in6 structure.
You can get the address bytes easily.
const uint8_t *bytes = ((const struct sockaddr_in6 *)addrPtr)->sin6_addr.s6_addr;
Then add 12 to the pointer because the 12 first bytes are not interesting (10 0x00, then 2 0xff). Only the 4 last ones mater.
bytes += 12;
Now, we can use those four bytes to do whatever we want. For example, we might store them into a IPv4 struct in_addr address.
struct in_addr addr = { *(const in_addr_t *)bytes };
Then we can get a string using inet_ntop (declared in ).
char buffer[16]; // 16 characters at max: “xxx.xxx.xxx.xxx” + NULL terminator
const char *string = inet_ntop(AF_INET, &addr, buffer, sizeof(buffer));
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