sending at commands with c++ on cubietruck -

i have cubieboard3 (cubietruck) , i'm trying send @ commands cb modem, i'm stuck on reading answer modem. c++ code:

#include <stdio.h> #include <string.h> #include <iostream> #include <unistd.h> #include <fcntl.h> #include <errno.h> #include <termios.h>  using namespace std;   int main(void) {   int fd; /* file descryptor port */    fd = open("/dev/ttys1", o_rdwr | o_noctty | o_ndelay);   if (fd == -1)//if not open port   {     perror("open_port: unable open /dev/ttys1 - ");   }   else //if port opened   {     fcntl(fd, f_setfl, fndelay);       //sending data     std::cout<<"port opened!"<<endl;     std::cout<<"sending 'atz\r' "<<endl;     int n = write(fd, "atz\r", 4);     if (n < 0)       fputs("write() of 4 bytes failed!\n", stderr);     else std::cout<<"data send!"<<endl;      //reading data     char buf [10];     int f = read(fd, buf, sizeof(buf));     if (f < 0) fputs("reading failed!\n", stderr);     else std::cout<<f<<endl;   }   return (fd); } 

and returns me :

port opened! sending atz data send! reading failed! 

what did wrong?

i changed fcntl(fd, f_setfl, fndelay); fcntl(fd, f_setfl, 0); , started read correctly, started sending kind of trash answer.