sockets - c++ winsock - server communicates only with single client while it should communicate with every client -

i writing single chat program gui. wanted write server accept many clients. every client can connect successfuly. there strange problem sending , receiving data. use select() , thread handle many sockets @ same time. if client sends data server, receive , send client (the client written without "prediction"). server won't send further clients (like every client had own private conversation server). here's code:

// rewritten beej's tutorial little , insignificant changes /* in thread */ fd_set mainfd; fd_set readfd; // sin-size, newfd, maxfd - int while(true) {     readfd = mainfd;     if(select(maxfd+1, &readfd, null, null, null) == -1)     {         messageboxa(null, "error while trying accept incoming connections (select)", "error", 16);         itoa(getlasterror(), buf, 10);         messageboxa(null, buf, buf, 0);         break;     }     for(int = 0; <= maxfd; i++)     {         char* psr;         char srmsg[256];         if(fd_isset(i, &readfd))         {             if(i == mainsocket)             {                 sin_size = sizeof(their_addr);                 newfd = accept(mainsocket, (struct sockaddr*)&their_addr, &sin_size);                 if(newfd == socket_error)                 {                     addtexttoedit(hstaticchat, "* error: couldn't accept incoming connection.", true);                 }                 else                 {                     fd_set(newfd, &mainfd);                     if(newfd > maxfd)                     {                         maxfd = newfd;                     }                  }             }             else             {                 len = recv(i, srmsg, 256, 0);                 if(len == 0 || len == socket_error)                 {                     addtexttoedit(hstaticchat, "* client has disconnected", true);                     close(i);                     fd_clr(i, &mainfd);                 }                 else                 {                         addtexttoedit(hstaticchat, srmsg, true);                         for(int j = 0; j <= maxfd; j++)                         {                           if(fd_isset(j, &readfd))                           {                                   send(j, srmsg, len, 0);                           }                         }                  }              }         }      } } 

you sending data clients whos fd in readfd, is, 1 communicated you. try test fd_isset(j, mainfd) instead.