코드좀 살펴봐주심 감사하겠읍니다

안녕하세요
리눅스처음공부하는 초짜입니다
다른고수님의 소스를 나름대로 조금 고쳤는데
에러가 무지많이나는군요
한번살펴봐주시면감사하겠읍니다

#include <sys/stat.h>

#include <time.h>
#include <sys/socket.h>
#include <signal.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/un.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>

// ------------------------------
// 전역 자료들
// ------------------------------
typedef struct clientdata
{
unsigned long int addr;
int port;
int start_time;
} clndata;

// 쓰레드 전역 함수들
void *thread_comm(void *);

int main(int argc, char **argv)
{
pthread_t p_thread;
struct sockaddr_in clientaddr, serveraddr;
char th_data[256];

int server_sockfd, client_sockfd, client_len;

memset(th_data, 0x00, 256);

if ((server_sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
{
perror("socket error : ");
exit(0);
}

bzero(&serveraddr, sizeof(serveraddr));
serveraddr.sin_family = AF_INET;
serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
serveraddr.sin_port = htons(atoi(argv[1]));

if (bind(server_sockfd, (struct sockaddr *)&serveraddr,
sizeof(serveraddr)) == -1)
{
perror("bind error : ");
exit(0);
}
if (listen(server_sockfd, 5) == -1)
{
perror("bind error : ");
exit(0);
}

// Client 의 연결을 받아들인다.
// 새로운 Client 가 들어오면 쓰레드를 생성시킨다.
// 이때 쓰레드 함수아규먼트로 Client 소켓지시자와 struct sockaddr_in
// 정보를 넘긴다.
while(1)
{
client_len = sizeof(clientaddr);
client_sockfd = accept(server_sockfd, (struct sockaddr *)&clientaddr,
(socklen_t *)&client_len);

// 쓰레드로 넘길 정보를 만든다.
// 0 .... 255
// th_data 의 구조
// +------+------------------+-----+
// |sockfd|struct sockaddr_in| |
// +------+------------------+-----+
memcpy(th_data, (void *)&client_sockfd, sizeof(client_sockfd));
memcpy(th_data+sizeof(client_sockfd), (void *)&clientaddr, client_len);

// 쓰레드 생성
if (pthread_create(&p_thread, NULL, thread_comm, (void *)th_data) == -1)
{
perror("thread Create error\n");
exit(0);
}

else
{
// cout << "Thread Create Success" << endl;
}
}
}

void *thread_comm(void *data)
{
int sockfd;
clndata clientinfo;

struct hostent *myent;
struct in_addr *myen;
long int *add;

struct sockaddr_in clientaddr;
int client_len = sizeof(clientaddr);
char buf[255];
char query[255];

pthread_t th;

// pthread_join 을 하지 않을것임으로
// detach 를 해줘서 쓰레드 종료시
// 쓰레드 자원을 정리할수 있도록 해줘야 한다.
pthread_detach(pthread_self());

memcpy((void *)&sockfd, (char *)data, sizeof(int));
memcpy((void *)&clientaddr, (char *)data+sizeof(int), client_len);

// 클라이언트 정보를 전역 자료에 입력한다.
// 입력되는 값은 주소(32bit), 포트, 연결시간이다.
clientinfo.addr = clientaddr.sin_addr.s_addr;
clientinfo.port = ntohs(clientaddr.sin_port);
time((time_t *)&clientinfo.start_time);

while(1)
{

if (read(sockfd, buf, 255) <= 0)
{
close(sockfd);
pthread_exit((void *)NULL);
}
if (strncmp(buf, "quit", 4) == 0)
{
write(sockfd, "bye bye", 8);
close(sockfd);
pthread_exit((void *)NULL);
}

// 그렇지 않을경우
sprintf(query, "./bindquery %s %s", buf,clientinfo.addr);

FILE *fp;
int state;

fp = popen(query, "r");
if (fp == NULL)
{
perror("erro : ");
exit(0);
}
state = pclose(fp);
myent = gethostbyname(buf);

while(*myent->h_addr_list != NULL)
{
add = (long int *)*myent->h_addr_list;
myen->s_addr = *add;
// printf("%s\n", inet_ntoa(*myen));
if(strcmp(clientinfo.addr,inet_ntoa(*myen) == 0)
{
write(sockfd, "query_ok", 255);
break;
}
myent->h_addr_list++;
}

close(sockfd);

write(sockfd, "end", 255);
memset(buf, 0x00, 255);
}
}

아래는 에러코드입니다
[root@ns1 root]# g++ -o aaa bindupdate.c -lpthread
bindupdate.c: In function `void* thread_comm(void*)':
bindupdate.c:159: `gethostbyname' undeclared (first use this function)
bindupdate.c:159: (Each undeclared identifier is reported only once for each 
   function it appears in.)
bindupdate.c:161: invalid use of undefined type `struct hostent'
bindupdate.c:102: forward declaration of `struct hostent'
bindupdate.c:163: invalid use of undefined type `struct hostent'
bindupdate.c:102: forward declaration of `struct hostent'
bindupdate.c:166: invalid conversion from `long unsigned int' to `const char*'
bindupdate.c:166: cannot convert `bool' to `const char*' for argument `2' to `
   int strcmp(const char*, const char*)'
bindupdate.c:167: parse error before `{' token
bindupdate.c:171: invalid use of undefined type `struct hostent'
bindupdate.c:102: forward declaration of `struct hostent'
bindupdate.c: At global scope:
bindupdate.c:180: parse error before `}' token
bindupdate.c:180:2: warning: no newline at end of file
[root@ns1 root]#