IPv6地址用冒号和16进制数表示，其中遇到连续的0可以作省略处理，如2001:0:0:0:0:0:0:1可以写成2001::1，这样对于书写很方便，但是带来一个额外的问题：两个地址比较的时候不能像IPv4那样调用字符串比较函数进行比较。本文通过比较两个IPv6地址的网络字节序来判断是否相等。
#include <stdio.h>
#include <arpa/inet.h>
int ipv6_equal(char *addr1, char *addr2)
{
int ret = -1;
int i = 0;
unsigned char n_addr1[16] = {-1};
unsigned char n_addr2[16] = {-1};
if (!addr1) {
printf("addr1 is NULL\n");
return -1;
}
if (!addr2) {
printf("addr2 is NULL\n");
return -1;
}
ret = inet_pton(AF_INET6, addr1, &(n_addr1));
if (ret <= 0 ) {
if (ret == 0) {
printf("addr1: Invalid IPv6 address\n");
}
return -1;
}
ret = inet_pton(AF_INET6, addr2, &(n_addr2));
if (ret <=0 ) {
if (ret == 0) {
printf("addr2: Invalid IPv6 address\n");
}
return -1;
}
for (i = 0; i < 16; i++) {
//printf("i: %d, addr1: %u, addr2: %u\n", i, n_addr1[i], n_addr2[i]);
if (n_addr1[i] != n_addr2[i]) {
return 1;
}
}
return 0;
}
int main(void)
{
if (ipv6_equal("2001::1", "2001::1") == 0) {
printf("test: 2001::1 equal 2001::1\n");
}
if (ipv6_equal("2001:0:0:0:0:0:0:1", "2001::1") == 0) {
printf("test: 2001:0:0:0:0:0:0:1 equal 2001::1\n");
}
if (ipv6_equal("2001::1", "2001::4") == 1) {
printf("test: 2001::1 not equal 2001::4\n");
}
if (ipv6_equal("2001:::1", "2001::4") == -1) {
printf("test: Invalid address\n");
}
return 0;
}
结果：
test: 2001::1 equal 2001::1
test: 2001:0:0:0:0:0:0:1 equal 2001::1
test: 2001::1 not equal 2001::4
addr1: Invalid IPv6 address
test: Invalid address