#include <winsock2.h>
#include <windows.h>
#include "resource.h"
#include "ya.h"

////////////////////////////////////////////////////////////////////////////////////////////////////

#define WM_CLIENTMSG   (WM_USER + 1)

////////////////////////////////////////////////////////////////////////////////////////////////////

BOOL StartWinsock() ;
BOOL CreateSocket(SOCKET *s) ;
void EndWinsock() ;
BOOL Select( HWND hwnd, SOCKET s, int Msg, int flag ) ;
BOOL Connect( char *pAddr, short port) ;
BOOL RecvMsg( SOCKET ClientSocket, char *recvbuff, HWND hwnd ) ;
BOOL SendMsg( SOCKET ClientSocket, char *sendbuff, int size) ;

////////////////////////////////////////////////////////////////////////////////////////////////////

SOCKET g_socket ;
char g_Buff[100] ;

char g_recvbuf[256] ;
int   g_bufsize ;

////////////////////////////////////////////////////////////////////////////////////////////////////


BOOL CALLBACK DlgProc(HWND hwnd, UINT iMsg, WPARAM wparam, LPARAM lparam) ;

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow)
{
        int ret ;
        
        if(!StartWinsock())
        {
                AfxMessageBox("StartWinsock() Error") ;
                return 0 ;
        }

        ret = DialogBox(hInstance, MAKEINTRESOURCE( IDD_DIALOG1 ), NULL, ( DLGPROC )DlgProc );
        if(ret != 0)
        {
                AfxMessageBox("StartWinsock() Error") ;
                EndWinsock() ;
                return 0 ;
        }

        EndWinsock() ;

        return 0 ;
}

BOOL CALLBACK DlgProc(HWND hwnd, UINT iMsg, WPARAM wparam, LPARAM lparam)
{
        char IPAddress[50] = {0,} ;
        HWND hListWnd ;
        short port ;

        switch(iMsg)
        {
        case WM_INITDIALOG :

                CreateSocket(&g_socket) ;
                Select(hwnd, g_socket, WM_CLIENTMSG, FD_CONNECT) ;
                SetWindowText(hwnd, "client") ;
                CenterWindow(hwnd) ;

                return TRUE ;
        case WM_COMMAND :

                switch(LOWORD(wparam))
                {
                case IDC_CONNECT :

                        if(g_socket == INVALID_SOCKET)
                        {
                                CreateSocket(&g_socket) ;
                                Select(hwnd, g_socket, WM_CLIENTMSG, FD_CONNECT | FD_READ) ;
                        }

                        GetDlgItemText( hwnd, IDC_ADDRESS, IPAddress, sizeof(IPAddress) );
                        port = GetDlgItemInt(hwnd, IDC_PORT, NULL, TRUE) ;
                        if( Connect( IPAddress, port ) )
                        {                                  
                                  if( WSAEWOULDBLOCK == WSAGetLastError() )
                                {
                                        hListWnd = GetDlgItem( hwnd, IDC_RECVLIST );
                                        SendLogMessage( hListWnd, "Server 접속이 대기중입니다..." );                                                          
                                }
                                else
                                {
                                        hListWnd = GetDlgItem( hwnd, IDC_RECVLIST );
                                        SendLogMessage( hListWnd, "Server 접속이 성공적입니다..." );                                                          
                                }
                        }
                        else
                        {
                                hListWnd = GetDlgItem( hwnd, IDC_RECVLIST );
                                SendLogMessage( hListWnd, "Server 접속에 실패 했습니다..." );                                                          
                        }        
                        return TRUE ;
                case IDC_DISCONNECT :

                        closesocket(g_socket) ;
                        g_socket = INVALID_SOCKET ;

                        return TRUE ;
                case IDC_SEND :

                        ZeroMemory( g_Buff, sizeof(g_Buff) );

                        if( GetDlgItemText( hwnd, IDC_MSGEDIT, g_Buff, sizeof(g_Buff) ) > 0 )
                        {                
                                SetDlgItemText(hwnd, IDC_MSGEDIT, "") ;
                                SendMsg( g_socket, g_Buff, strlen(g_Buff));
                        }

                        break ;
                case IDCANCEL :

                        EndDialog(hwnd, FALSE) ;

                        return TRUE ;
                }
                return TRUE ;
        case WM_CLIENTMSG :                
          
                switch( WSAGETSELECTEVENT(lparam) )
                {
                case FD_CONNECT :                  
                
                        Select( hwnd, g_socket, WM_CLIENTMSG, FD_READ | FD_CLOSE );
                        hListWnd = GetDlgItem( hwnd, IDC_RECVLIST );
                                        
                        return TRUE ;
                case FD_READ :  

                        hListWnd = GetDlgItem( hwnd, IDC_RECVLIST );
                         RecvMsg( wparam, g_recvbuf, hListWnd );
                        SendLogMessage( hListWnd, "%s", g_recvbuf );

                        return TRUE ;
                case FD_CLOSE :

                        hListWnd = GetDlgItem( hwnd, IDC_RECVLIST );
                        SendLogMessage( hListWnd, "%s", "Server 가 종료 되었습니다"  );
                        closesocket(g_socket) ;
                        g_socket = INVALID_SOCKET ;

                        return TRUE ;                                                
                }
                return TRUE;
        }
        return FALSE ;
}

BOOL StartWinsock( )
{
     WSADATA wsd;
     int ret;
    
     //소켓 라이브러리 초기화
     ret = WSAStartup( MAKEWORD(2,2), &wsd );
     if( ret == SOCKET_ERROR )
     {
          AfxMessageBox( "StartWinSock() -> WSAStartup( ) 함수 실패... " );
          return FALSE;
     }
    
     return TRUE;
}

BOOL CreateSocket(SOCKET *s)
{
        *s = socket( AF_INET, SOCK_STREAM, 0 );
    if( g_socket == INVALID_SOCKET )
    {
         AfxMessageBox( "StartWinSock() -> socket( ) 함수 실패... " );
         return FALSE;
    }    
    
    return TRUE;
}


void EndWinsock( )
{
    if( g_socket )
        closesocket( g_socket );
    
    WSACleanup( );
}

BOOL Select( HWND hwnd, SOCKET s, int Msg, int flag )
{
        int  ret;

        ret = WSAAsyncSelect( s, hwnd, Msg, flag );
        if( ret == SOCKET_ERROR )
        {
          AfxMessageBox( "Select() -> WSAAsyncSelect( ) 함수 실패... " );
          return FALSE;
        }

        return TRUE;
}

BOOL Connect( char *pAddr, short port )
{
        struct hostent*    host;
    struct sockaddr_in sa;
        int    ret;    

        host = gethostbyname( pAddr );
        
        ZeroMemory( &sa, sizeof(sa) );
        sa.sin_family      = AF_INET;
        sa.sin_port        = htons(port);         
//        sa.sin_addr.s_addr = inet_addr( pAddr );  
여기서 에러 ->sa.sin_addr        = *((struct in_addr *)host->h_addr_list[0]);            
        
        ret = connect( g_socket, (struct sockaddr *)&sa, sizeof(struct sockaddr));
        if( ret == SOCKET_ERROR )
        {
                if( WSAEWOULDBLOCK == WSAGetLastError() )
                        return TRUE;

                return FALSE;
        }
        return TRUE;
}

BOOL RecvMsg( SOCKET ClientSocket, char *recvbuf, HWND hwnd )
{    
        unsigned long recvsize, i ;
        int           recvbyte;        


        if( (ioctlsocket( ClientSocket, FIONREAD, &recvsize ) == 0 ) && (recvsize > 0 ) )
        {
                if( recvbuf != NULL )
                        ZeroMemory( g_recvbuf, 256 );
                
                for( i = 0; i < recvsize; )
                {
                        recvbyte = recv( ClientSocket, recvbuf + i, recvsize, 0 );            
                        if( recvbyte > 0 )
                        {
                                i += (unsigned long)recvbyte;
                                recvsize = recvsize - recvbyte ;
                        }
                        else
                        {

                        }
                }
        }

    return TRUE;
}

BOOL SendMsg( SOCKET ClientSocket, char *sendbuff, int size )
{        
        int ret;

        ret = send( ClientSocket, sendbuff, size, 0 );
        if( ret == SOCKET_ERROR )              
        {  
                AfxMessageBox( "SendMsg() -> send( ) 함수 실패... " );
                return FALSE;
        }

        return TRUE;

}

강사님이 이해하라고 쳐준 소스인데 저 부분에서 에러가 납니다.
왜 에러가 나는지 이유를 몰라서 그럽니다.