c++ - non-blocking recv returns 0 when disconnected -

i'm trying 'catch' when disconnect happens. don't what's wrong. recv() returns 0, errno set 0 , ioctl returns 0. searching 6 hours on web without success. can tell me what's wrong?

regards.

bool network::setblocking(bool blocking) {     // sets blocking or non-blocking mode.      int flags = blocking ? 1 : 0;      return ioctl(this->sockfd, fionbio, &flags) ? false : true; }  networkstatus network::status() {     // returns socket status.      struct timeval tv;     fd_set  fd;     int result = 0;      tv.tv_sec  = 3;     tv.tv_usec = 0;      fd_zero(&fd);     fd_set(this->sockfd, &fd);      result = select(this->sockfd + 1, &fd, 0, 0, &tv);      if(result == -1)     {         return network_error;     }     else if(result)     {         return network_readyread;     }     else     {         return network_timeout;     } }  int network::bytesavailable() {     // returns number of bytes available.      int bytes = 0;      if(ioctl(this->sockfd, fionread, &bytes) < 0 || errno)     {         return -1;     }      return bytes; }  int network::read(char *buffer, int size) {     // reads data socket.      return recv(this->sockfd, buffer, size, 0); } ... int main(int argc, char* argv[]) {     network net;     ...     while(true)     {         switch(net.status())         {             ...             case network_readyread:             {                 int bytesavailable = net.bytesavailable();                 char temp[bytesavailable];                 int len = net.read(temp, bytesavailable);                 printf("len: %d\nerrno: %d\nbytesavailable: %d\n", len, errno, bytesavailable); // len: 0, errno: 0, bytesavailable: 0                 break;             }         }     } // status     return 0; } 

when other side close socket or shutdown(send), @ side select return socket readable, select command return 1 indicating there data read (in fact there no data, signal indicating socket closed), ioctl return 0 bytes available , recv() return 0 , that's how tcp works. in program should take care of bytesavaliable returns 0 and/or read() returns 0. in these cases socket has been closed , should close side , waits (accept) or establish (connect) new connection.

edit: add commnents:

well, not exactly. when recv() = 0, socket closed or shutdown send, when = -1 there error in socket. if socket non-blocking (has o_nonblock set) should check error (errno on unix, wsagetlasterror() on windows) , ewouldblock or eagain indicates there no data available , socket still valid. also, in rare cases, recv() return -1 , error eintr means during recv() operation interrupt (signal) has been received, in case should ignore error (unless waiting such signal) , reissue recv().

ret=recv(socket, buff, length, 0); if (ret > 0)  {     // data has been received } else if (ret == 0)  {     // socket has been closed or shutdown send } else {    // there error, let's see    int error = errno; // or wsagetlasterror()    switch (error)    {          case eagain:          case ewouldblock:                // socket o_nonblock , there no data available               break;          case eintr:                // interrupt (signal) has been catched               // should ingore in cases               break;          default:               // socket has error, no valid anymore               return;    } } 

saying that, 1 thing must clear if recv() return 0 or -1 socket not valid anymore , should closed, again, depends on many factors, protocol use keep dialog between sockets, if in non-blocking, etc. example, other side issue shutdown(); in case recv() return 0 still send() through socket without errors.