Linux下gethostbyname_h_addr_list_linux gethostbyname h_addr

  struct hostent
{
  char* h_name;
  char** h_aliases;
  short h_addrtype;
  short h_length;
  char**h_addr_list;
};


//linux
#include<netdb.h>
struct hostent *  gethostbyname(const char*hostname);
error:return NULL and set  h_errno

//compile:gcc gethostbyname.c
//run:./a.out
#include<stdio.h>
#include<netdb.h>
#include<unistd.h>
#include<string.h>
int main(int argc,char* argv[])
{
    char ret_hostname[65];
    gethostname(ret_hostname,sizeof(ret_hostname));;//#include<unistd.h>
    printf("by gethostname() get hostname:%s\n",ret_hostname);
    
    struct hostent *ret_hostent;
 ret_hostent=gethostbyname(ret_hostname);
 printf("h_name %s\nh_aliases %s\nh_addrtype %d\nh_length %d\nh_addr_list %s\n",
               ret_hostent->h_name,         
                               *(ret_hostent->h_aliases),
                                             ret_hostent->h_addrtype,
                                                          ret_hostent->h_length,
                                                                          *(ret_hostent->h_addr_list+1));
printf("sizeof(h_addr_list[0]) is %lu\n",sizeof(ret_hostent->h_addr_list[0]));//long unsigned int
printf("strlen(h_addr_list[0]) is %zu\n",strlen(ret_hostent->h_addr_list[0]));//size_t
//type:  int   char   char*     unsigned int       long unsigned int      size_t   float   double    long int   
//format:%d    %c      %s        %u                   %lu                  %zu     %f       %lf       %ld
 
printf("%d %d %d %d\n",ret_hostent->h_addr_list[0][0]&0xFF,ret_hostent->h_addr_list[0][1]&0xFF,ret_hostent->h_addr_list[0][2]&0xFF,
               ret_hostent->h_addr_list[0][3]&0xFF);//big_endian
return 0;}
 
/*
  struct hostent
{
  char* h_name;
  char** h_aliases;
  short h_addrtype;
  short h_length;
  char**h_addr_list;
};
//linux
#include<netdb.h>
struct hostent *  gethostbyname(const char*hostname);
error:return NULL and set  h_errno
*/

ubuntu@linuxc_easy:~/linuxc_easy/pcdtest$ gcc gethostbyname.c                                                                                                             
ubuntu@linuxc_easy:~/linuxc_easy/pcdtest$ ./a.out                                                                                                                         
by gethostname() get hostname:linuxc_easy                                                                                                                                 
h_name linuxc_easy                                                                                                                                                        
h_aliases (null)                                                                                                                                                          
h_addrtype 2                                                                                                                                                              
h_length 4                                                                                                                                                                
h_addr_list (null)                                                                                                                                                        
sizeof(h_addr_list[0]) is 8                                                                                                                                               
strlen(h_addr_list[0]) is 2                                                                                                                                               
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