[Network] DNS nslookup 프로그램 예제

#include <stdio.h>
#include <winsock2.h>
 
void first();
void run();
 
int main(){
    WSADATA wsdata;
    WSAStartup(MAKEWORD(2,2), &wsdata);
    first();
    while(1)
        run();
    WSACleanup();
    return 0;
}
void first(){
    HOSTENT *host;
    host = gethostbyname("kns.kornet.net");
    printf("기본 서버: %s\n", host->h_name);
    printf("Address:  %s\n\n", inet_ntoa(*(IN_ADDR*)host->h_addr_list[0]));
}
void run(){
    printf("\n> ");
    char url[30];
    scanf("%s", url);
    if(strcmp(url , "exit") == 0)
        exit(0);
    first();
    HOSTENT *runhost;
    if(inet_addr(url) == INADDR_NONE) // 입력받은 값이 url 주소라면
        runhost = gethostbyname(url);
    else{
        SOCKADDR_IN addr; 
        addr.sin_addr.s_addr = inet_addr(url);
        runhost = gethostbyaddr((CHAR*)&addr.sin_addr, 4, AF_INET);
    }
    printf("권한 없는 응답 : \n");
    printf("이름: \t%s\n", runhost->h_name);
    printf("Addresses:");
    for(int i=0; runhost->h_addr_list[i]; i++)
        printf("\t%s\n", inet_ntoa(*(IN_ADDR*)runhost->h_addr_list[i]) );
}