getaddrinfo使用

getaddrinfo根据域名获取IP等信息。

头文件

#include  
     #include  
     #include  
     

函数原型

int getaddrinfo(const char *node, const char *service, const struct addrinfo *hints, struct addrinfo **res); void freeaddrinfo(struct addrinfo *res); const char *gai_strerror(int errcode); 

注意在使用getaddrinfo时，const struct addrinfo *hints优先配置SOCK_STREAM域，SOCK_DGRAM有失败的情况。

addrinfo 结构体定义

struct addrinfo { 
    int ai_flags; int ai_family; int ai_socktype; int ai_protocol; size_t ai_addrlen; struct sockaddr *ai_addr; char *ai_canonname; struct addrinfo *ai_next; }; 

示例1：只取第一个IP地址

#include  
     #include  
     #include  
     #include  
     #include  
    //结构体addrinfo, in_addr #include  
     #include  
     using namespace std; int main(){ 
    char* hostname = "www.cnblogs.com";//博客园的网址，返回实际IP地址 addrinfo hints, *res; in_addr addr; int err; memset(&hints, 0, sizeof(addrinfo)); hints.ai_socktype = SOCK_STREAM; hints.ai_family = AF_INET; if((err = getaddrinfo(hostname, NULL, &hints, &res)) != 0){ 
    printf("error %d : %s\n", err, gai_strerror(err)); return 1; } addr.s_addr = ((sockaddr_in*)(res->ai_addr))->sin_addr.s_addr; printf("ip addresss: %s\n", inet_ntoa(addr));//博客园的网址，返回实际IP地址 freeaddrinfo(res); return 0; } 

示例2：显示所有域名查找到的所有IP地址

#include  
     #include  
     #include  
     #include  
     #include  
     #include  
     #include  
     #include  
    //结构体addrinfo, in_addr #include  
     #include  
     using namespace std; int main(int argc, char **argv){ 
    char *hostname; struct addrinfo hints,*result, *rp; int err; in_addr addr; //没有输入域名时，博客园的网址，返回实际IP地址 hostname = argc < 2 ? (char *)"www.cnblogs.com" : argv[1]; memset(&hints, 0, sizeof(addrinfo)); hints.ai_socktype = SOCK_STREAM; hints.ai_family = AF_INET; if((err = getaddrinfo(hostname, NULL, &hints, &result)) != 0){ 
    printf("error %d : %s\n", err, gai_strerror(err)); return 1; } for (rp = result; rp != NULL; rp = rp->ai_next) { 
    addr.s_addr = ((sockaddr_in*)(rp->ai_addr))->sin_addr.s_addr; printf("ip addresss: %s\n", inet_ntoa(addr)); } freeaddrinfo(result); return 0; } 

一遍都会输出两个IP地址，如www.baidu.com；

示例3：

Server program：

#include  
     #include  
     #include  
     #include  
     #include  
     #include  
     #include  
     #define BUF_SIZE 500 int main(int argc, char *argv[]) { 
    struct addrinfo hints; struct addrinfo *result, *rp; int sfd, s; struct sockaddr_storage peer_addr; socklen_t peer_addr_len; ssize_t nread; char buf[BUF_SIZE]; if (argc != 2) { 
    fprintf(stderr, "Usage: %s port\n", argv[0]); exit(EXIT_FAILURE); } memset(&hints, 0, sizeof(struct addrinfo)); hints.ai_family = AF_UNSPEC; /* Allow IPv4 or IPv6 */ hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */ hints.ai_flags = AI_PASSIVE; /* For wildcard IP address */ hints.ai_protocol = 0; /* Any protocol */ hints.ai_canonname = NULL; hints.ai_addr = NULL; hints.ai_next = NULL; s = getaddrinfo(NULL, argv[1], &hints, &result); if (s != 0) { 
    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s)); exit(EXIT_FAILURE); } /* getaddrinfo() returns a list of address structures. Try each address until we successfully bind(2). If socket(2) (or bind(2)) fails, we (close the socket and) try the next address. */ for (rp = result; rp != NULL; rp = rp->ai_next) { 
    sfd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol); if (sfd == -1) continue; if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0) break; /* Success */ close(sfd); } if (rp == NULL) { 
    /* No address succeeded */ fprintf(stderr, "Could not bind\n"); exit(EXIT_FAILURE); } freeaddrinfo(result); /* No longer needed */ /* Read datagrams and echo them back to sender */ for (;;) { 
    peer_addr_len = sizeof(struct sockaddr_storage); nread = recvfrom(sfd, buf, BUF_SIZE, 0, (struct sockaddr *) &peer_addr, &peer_addr_len); if (nread == -1) continue; /* Ignore failed request */ char host[NI_MAXHOST], service[NI_MAXSERV]; s = getnameinfo((struct sockaddr *) &peer_addr, peer_addr_len, host, NI_MAXHOST, service, NI_MAXSERV, NI_NUMERICSERV); if (s == 0) printf("Received %zd bytes from %s:%s\n", nread, host, service); else fprintf(stderr, "getnameinfo: %s\n", gai_strerror(s)); if (sendto(sfd, buf, nread, 0, (struct sockaddr *) &peer_addr, peer_addr_len) != nread) fprintf(stderr, "Error sending response\n"); } } 

Client program

#include  
     #include  
     #include  
     #include  
     #include  
     #include  
     #include  
     #define BUF_SIZE 500 int main(int argc, char *argv[]) { 
    struct addrinfo hints; struct addrinfo *result, *rp; int sfd, s, j; size_t len; ssize_t nread; char buf[BUF_SIZE]; if (argc < 3) { 
    fprintf(stderr, "Usage: %s host port msg...\n", argv[0]); exit(EXIT_FAILURE); } /* Obtain address(es) matching host/port */ memset(&hints, 0, sizeof(struct addrinfo)); hints.ai_family = AF_UNSPEC; /* Allow IPv4 or IPv6 */ hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */ hints.ai_flags = 0; hints.ai_protocol = 0; /* Any protocol */ s = getaddrinfo(argv[1], argv[2], &hints, &result); if (s != 0) { 
    fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s)); exit(EXIT_FAILURE); } /* getaddrinfo() returns a list of address structures. Try each address until we successfully connect(2). If socket(2) (or connect(2)) fails, we (close the socket and) try the next address. */ for (rp = result; rp != NULL; rp = rp->ai_next) { 
    sfd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol); if (sfd == -1) continue; if (connect(sfd, rp->ai_addr, rp->ai_addrlen) != -1) break; /* Success */ close(sfd); } if (rp == NULL) { 
    /* No address succeeded */ fprintf(stderr, "Could not connect\n"); exit(EXIT_FAILURE); } freeaddrinfo(result); /* No longer needed */ /* Send remaining command-line arguments as separate datagrams, and read responses from server */ for (j = 3; j < argc; j++) { 
    len = strlen(argv[j]) + 1; /* +1 for terminating null byte */ if (len > BUF_SIZE) { 
    fprintf(stderr, "Ignoring long message in argument %d\n", j); continue; } if (write(sfd, argv[j], len) != len) { 
    fprintf(stderr, "partial/failed write\n"); exit(EXIT_FAILURE); } nread = read(sfd, buf, BUF_SIZE); if (nread == -1) { 
    perror("read"); exit(EXIT_FAILURE); } printf("Received %zd bytes: %s\n", nread, buf); } exit(EXIT_SUCCESS); } 

getaddrinfo函数ipv6的应用
https://blog.csdn.net/u0/article/details/

参考资料
https://www.cnblogs.com/xiaoshiwang/p/9763825.html
http://www.man7.org/linux/man-pages/man3/getaddrinfo.3.html
https://blog.csdn.net/fanx021/article/details/
https://blog.csdn.net/u0/article/details/
https://blog.csdn.net/jctian000/article/details/