原文链接:
http://blog.chinaunix.net/uid-26583794-id-3167485.html
addrinfo结构体的定义如下:
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struct addrinfo {
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int ai_flags; /* customize behavior */
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int ai_family; /* address family */
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int ai_socktype; /* socket type */
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int ai_protocol; /* protocol */
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socklen_t ai_addrlen; /* length in bytes of address */
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struct sockaddr *ai_addr; /* address */
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char *ai_canonname; /* canonical name of host */
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struct addrinfo *ai_next; /* next in list */
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.
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.
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.
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};
ai_family指定了地址族,可取值如下:
AF_INET 2 IPv4
AF_INET6 23 IPv6
AF_UNSPEC 0 协议无关
ai_socktype指定我套接字的类型
SOCK_STREAM 1 流
SOCK_DGRAM 2 数据报
在AF_INET通信域中套接字类型SOCK_STREAM的默认协议是TCP(传输控制协议)
在AF_INET通信域中套接字类型SOCK_DGRAM的默认协议是UDP(用户数据报协议)
ai_protocol指定协议类型。可取的值取决于ai_address和ai_socktype的值
ai_flags指定了如何来处理地址和名字,可取值如下:
getaddrinfo函数 定义及需要的头文件如下:
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#include <sys/socket.h>
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#include <netdb.h>
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int getaddrinfo(const char *restrict host,
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const char *restrict service,
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const struct addrinfo *restrict hint,
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struct addrinfo **restrict res);
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Returns: 0 if OK, nonzero error code on error
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void freeaddrinfo(struct addrinfo *ai);
getaddrinfo函数允许将一个主机名字和服务名字映射到一个地址。
使用示例如下:
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#include<stdio.h>
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#include<stdlib.h>
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#include <netdb.h>
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#include <arpa/inet.h>
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void
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print_family(struct addrinfo *aip)
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{
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printf(" family ");
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switch (aip->ai_family) {
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case AF_INET:
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printf("inet");
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break;
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case AF_INET6:
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printf("inet6");
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break;
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case AF_UNIX:
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printf("unix");
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break;
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case AF_UNSPEC:
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printf("unspecified");
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break;
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default:
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printf("unknown");
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}
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}
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void
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print_type(struct addrinfo *aip)
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{
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printf(" type ");
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switch (aip->ai_socktype) {
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case SOCK_STREAM:
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printf("stream");
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break;
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case SOCK_DGRAM:
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printf("datagram");
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break;
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case SOCK_SEQPACKET:
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printf("seqpacket");
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break;
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case SOCK_RAW:
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printf("raw");
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break;
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default:
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printf("unknown (%d)", aip->ai_socktype);
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}
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}
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void
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print_protocol(struct addrinfo *aip)
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{
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printf(" protocol ");
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switch (aip->ai_protocol) {
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case 0:
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printf("default");
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break;
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case IPPROTO_TCP:
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printf("TCP");
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break;
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case IPPROTO_UDP:
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printf("UDP");
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break;
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case IPPROTO_RAW:
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printf("raw");
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break;
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default:
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printf("unknown (%d)", aip->ai_protocol);
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}
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}
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void
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print_flags(struct addrinfo *aip)
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{
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printf("flags");
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if (aip->ai_flags == 0) {
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printf(" 0");
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} else {
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if (aip->ai_flags & AI_PASSIVE)
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printf(" passive");
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if (aip->ai_flags & AI_CANONNAME)
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printf(" canon");
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if (aip->ai_flags & AI_NUMERICHOST)
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printf(" numhost");
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#if defined(AI_NUMERICSERV)
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if (aip->ai_flags & AI_NUMERICSERV)
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printf(" numserv");
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#endif
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#if defined(AI_V4MAPPED)
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if (aip->ai_flags & AI_V4MAPPED)
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printf(" v4mapped");
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#endif
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#if defined(AI_ALL)
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if (aip->ai_flags & AI_ALL)
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printf(" all");
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#endif
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}
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}
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int
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main(int argc, char *argv[])
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{
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struct addrinfo *ailist, *aip;
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struct addrinfo hint;
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struct sockaddr_in *sinp;
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const char *addr;
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int err;
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char abuf[INET_ADDRSTRLEN];
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if (argc != 3)
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printf("usage: %s nodename service", argv[0]);
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hint.ai_flags = AI_CANONNAME;
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hint.ai_family = 0;
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hint.ai_socktype = 0;
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hint.ai_protocol = 0;
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hint.ai_addrlen = 0;
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hint.ai_canonname = NULL;
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hint.ai_addr = NULL;
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hint.ai_next = NULL;
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if ((err = getaddrinfo(argv[1], argv[2], &hint, &ailist)) != 0)
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printf("getaddrinfo error: %s", gai_strerror(err));
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for (aip = ailist; aip != NULL; aip = aip->ai_next) {
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print_flags(aip);
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print_family(aip);
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print_type(aip);
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print_protocol(aip);
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printf("\n\thost %s", aip->ai_canonname?aip->ai_canonname:"-");
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if (aip->ai_family == AF_INET) {
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sinp = (struct sockaddr_in *)aip->ai_addr;
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addr = inet_ntop(AF_INET, &sinp->sin_addr, abuf,INET_ADDRSTRLEN);
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printf(" address %s", addr?addr:"unknown");
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printf(" port %d", ntohs(sinp->sin_port));
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}
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printf("\n");
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}
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exit(0);
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}
代码说明:sinp = (struct sockaddr_in *)aip->ai_addr;会将struct sockaddr 变量强制转化为struct sockaddr_in 类型
inet_ntop函数用于在二进制格式与点分十进制格式表示(a.b.c.d)之间进行转换
执行结果:#./a X86-PC nfs
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root@X86-PC:/home/cheney/work-link/linux_C_Test/linux-program/fig16# ./a X86-PC nfs
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flags canon family inet type stream protocol TCP
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host X86-PC address 127.0.1.1 port 2049
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flags canon family inet type datagram protocol UDP
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host - address 127.0.1.1 port 2049
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root@X86-PC:/home/cheney/work-link/linux_C_Test/linux-program/fig16#
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