gethostbyname 和 gethostbyaddr 的用法示例

gethostbyname 和 gethostbyaddr 函数声明如下：
#include
struct hostent *gethostbyname(const char *nmae);
//返回：成功则为非NULL指针，若出错则为NULL指针，同时设置h_errno.
struct hostent *gethostbyaddr(const char *addr, int len, 0);
//返回：成功则为非NULL指针，若出错则为NULL指针，同时设置h_errno.

结构体hostent

/* DNS host entry structure */
 struct hostent {
     char *h_hname;
     char **h_aliases;
     int h_addrtype;
     int h_length;
     char **h_addr_list;
 }

示例代码如下：

#include
 #include
 #include
 #include
 #include

 int main(int argc, char * argv[])
 {
     char **pp;
    struct in_addr addr;
     struct hostent *hostp;

     if(argc != 2) {
         fprintf(stderr, "usage: %s \n", argv[0]);
         exit(0);
     }

     if(inet_aton(argv[1], &addr))
         hostp = gethostbyaddr((const char *)&addr, sizeof(addr), AF_INET);
     else
         hostp = gethostbyname(argv[1]);

     printf("official hostname: %s\n", hostp->h_name);

     for(pp = hostp->h_aliases; *pp != NULL; pp++) {
         printf("alias: %s\n", *pp);
     }

     for(pp = hostp->h_addr_list; *pp != NULL; pp++) {
         //addr.s_addr = ((struct in_addr *)*pp)->s_addr;
         addr.s_addr = *(unsigned int *)*pp;
         printf("address: %s\n", inet_ntoa(addr));
     }


 }

 
编译
执行结果如下：
[root@CTOServer001 testprogram]# gcc -g exam002.c -o exam002
[root@CTOServer001 testprogram]# ./exam002 
official hostname:
alias:
address: 119.75.217.109
address: 119.75.218.70
[root@CTOServer001 testprogram]# ./exam002  127.0.0.1
official hostname: localhost
alias: localhost.localdomain
alias: localhost4
alias: localhost4.localdomain4
address: 127.0.0.1
[root@CTOServer001 testprogram]#