Linux下C/C++怎样通过主机名获得IP?

[ysxin]

各位高手：
求getaddrbyhost()函数使用例子，求下面这个代码反过来的，通过主机名获得IP：

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

int main(int argc, char **argv)
{
        struct hostent *ip;
        unsigned long hostname;

        if (argc != 2)
        {
                printf("Need to specify an IP address.\n");
                return -1;
        }
        if ((hostname = inet_addr(argv[1])) == -1)
        {
                printf("Could not find %s\n", argv[1]);
                return -1;
        }
        else
        {
                printf("hostname : %ld\n", hostname);
        }
        if ((ip = gethostbyaddr((char *)&hostname, sizeof(long), AF_INET)) != NULL)
                printf("%s is %s\n", argv[1], ip->h_name);
        else
                printf("Could not resolve %s\n", argv[1]);
        return 0;
}

[pathuang68]

[Quote=引用楼主 的回复:]
各位高手：
求getaddrbyhost()函数使用例子，求下面这个代码反过来的，通过主机名获得IP：
C/C++ code

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <net……
[/Quote]

用gethostbyname这个函数就行了。

[qq120848369]

struct hostent *gethostbyname(const char *name);

#include <sys/socket.h> /* for AF_INET */
struct hostent *gethostbyaddr(const void *addr,
socklen_t len, int type);


这些都是淘汰的函数了，只支持IPV4。

SYNOPSIS
       #include <sys/types.h>
       #include <sys/socket.h>
       #include <netdb.h>

       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);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getaddrinfo(), freeaddrinfo(), gai_strerror():
           _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE

DESCRIPTION
       Given  node and service, which identify an Internet host and a service, getaddrinfo() returns one or more addrinfo structures, each of which contains an
       Internet address that can be specified in a call to bind(2) or connect(2).  The getaddrinfo() function combines the functionality provided by  the  get-
       servbyname(3) and getservbyport(3) functions into a single interface, but unlike the latter functions, getaddrinfo() is reentrant and allows programs to
       eliminate IPv4-versus-IPv6 dependencies.

       The addrinfo structure used by getaddrinfo() contains the following fields:

           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;
           };

getaddrinfo一个函数全部搞定，给ip得Canonical name，给域名得IP。

但是别指望根据IP得到域名，这个功能是木有的，只能得到Canonical name和Alias，都是无用的。