从 struct addrinfo 中获取 IP 地址（作为字符串）

Question

我有一个

struct addrinfo

，这是为了建立联系而传递的：

struct addrinfo* address;
...
int fd = socket(address->ai_family, address->ai_socktype, address->ai_protocol);
...
int res = ::connect(fd, address->ai_addr, address->ai_addrlen);

如果连接成功，我想记录目标IP地址。

如何从这个结构中提取 IP 地址（作为要记录的字符串）？谷歌搜索结果只给出

getaddrinfo()

的结果。

Answer 1

您可以使用

inet_ntop

将 IPv4 或 IPv6 地址转换为字符串。

char addr[INET6_ADDRSTRLEN];
if (inet_ntop(address->ai_family, address->ai_addr, addr, address->ai_addrlen)) {
    printf("address=%s\n", addr);
} else {
    perror("invalid address");
}

Answer 2

你可以使用 [Man7]: INET_NTOP(3):

1. Cast ai_addr成员到sockaddr_in（或sockaddr_in6）结构

2. 在（上）结构的sin_addr（sin6_addr）成员上调用inet_ntop

code00.c:

#include <arpa/inet.h>
#include <netdb.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>


int main()
{
    struct addrinfo *pai = NULL;
    int err = getaddrinfo("www.example.com", NULL, NULL, &pai);
    if (err != 0) {
        fprintf(stderr, "error in getaddrinfo: %s\n", gai_strerror(err));
        return -1;
    }
    if (pai->ai_family == AF_INET) {
        struct sockaddr_in *psai = (struct sockaddr_in*)pai->ai_addr;
        char ip[INET_ADDRSTRLEN];
        if (inet_ntop(pai->ai_family, &(psai->sin_addr), ip, INET_ADDRSTRLEN) != NULL) {
            printf("IP: %s\n", ip);
        }
    } else if (pai->ai_family == AF_INET6) {
        struct sockaddr_in6 *psai = (struct sockaddr_in6*)pai->ai_addr;
        char ip[INET6_ADDRSTRLEN];
        if (inet_ntop(pai->ai_family, &(psai->sin6_addr), ip, INET6_ADDRSTRLEN) != NULL) {
            printf("IP: %s\n", ip);
        }
    } else {
        printf("Don't know how to convert family %d addresses\n", pai->ai_family);
    }
    freeaddrinfo(pai);
    printf("\nDone.\n\n");
    return 0;
}

输出：

[cfati@cfati-5510-0:/mnt/e/Work/Dev/StackExchange/StackOverflow/q075843180]> ~/sopr.sh
### Set shorter prompt to better fit when pasted in StackOverflow (or other) pages ###

[064bit prompt]> gcc -o main00.exe main00.c
[064bit prompt]> ./main00.exe
IP: 93.184.216.34

Done.

Answer 3

要从 C 中的

struct addrinfo

中提取 IP 地址（作为字符串），您可以使用

inet_ntop()

函数。这是一个如何使用它的例子：

#include <arpa/inet.h>

struct addrinfo* address;
// assume that address is initialized and used to create a socket

char ipstr[INET6_ADDRSTRLEN];
void* addr;

if (address->ai_family == AF_INET) { // IPv4
    struct sockaddr_in *ipv4 = (struct sockaddr_in *)address->ai_addr;
    addr = &(ipv4->sin_addr);
} else { // IPv6
    struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)address->ai_addr;
    addr = &(ipv6->sin6_addr);
}
// convert the IP address to a string
inet_ntop(address->ai_family, addr, ipstr, sizeof ipstr);

// log the IP address
printf("The destination IP address is: %s\n", ipstr);

此代码使用 inet_ntop() 函数将 struct addrinfo 的 ai_addr 字段中的二进制 IP 地址转换为字符串表示形式（IPv4 或 IPv6，具体取决于 ai_family 字段）。结果字符串存储在 ipstr 数组中，可以根据需要记录或打印。