求教套接字收发的问题

Question

本人写了如下的收发程序：
但每次接收的字数不对，只能收到四个字符？是何缘故？{
CBroadCastDlg* dlg=(CBroadCastDlg*)AfxGetApp()->GetMainWnd();
char buf[4096];
    int len=sizeof(dlg->client);

    while(1)
{
      memset(buf,0,sizeof(buf));
int result=recvfrom(dlg->sock,buf,sizeof(buf)-1,0,(sockaddr*)&(dlg->client),&len);

if(result==SOCKET_ERROR)
{
AfxMessageBox("receive");
return -1;
}
   
        dlg->m_revc.Format("%s",buf);
  
AfxMessageBox(dlg->m_revc);


}
return 0;
}
{
int length;
char* buf;

CString str;
GetDlgItemText(IDC_EDIT1,str);
buf=str.GetBuffer(0);
sockaddr_in to;
to.sin_family=PF_INET;
to.sin_addr.s_addr=INADDR_BROADCAST; to.sin_port=htons(PortNum);

buf[str.GetLength()]=0;
   
if((length=sendto(sock,buf,sizeof(buf),0,(LPSOCKADDR)&to,sizeof(SOCKADDR)))==SOCKET_ERROR)
{
AfxMessageBox("发送出错");
closesocket(sock);
return;
}
 AfxMessageBox(buf);

}

Answer 1

sendto(sock,buf,sizeof(buf),0,(LPSOCKADDR)&to,sizeof(SOCKADDR))一句中的sizeof(buf)等于4(指针的长度为4),所以只能发送4个bytes