Serial port in c++ , Unix - c++

Question

I wrote a code to connect, throught a serial port, mi computer to arduino.
This is arduino's code:
#include <Servo.h>
Servo servo;
const int pinServo = 2;
unsigned int angle;
void setup()
{
Serial.begin(9600);
servo.attach(pinServo);
servo.write(0);
}
void loop()
{
if(Serial.available()>0)
{
angle = Serial.read();
if(angle <= 179)
{
servo.write(angle);
}
}
}
And this is c++'s:
#include <iostream>
#include <unistd.h>
#include <fstream>
#include <termios.h>
using namespace std;
int main()
{
unsigned int angle;
ofstream arduino;
struct termios ttable;
cout<<"\n\ntest1\n\n";
arduino.open("/dev/tty.usbmodem3a21");
cout<<"\n\ntest2\n\n";
if(!arduino)
{
cout<<"\n\nERR: could not open port\n\n";
}
else
{
if(tcgetattr(arduino,&ttable)<0)
{
cout<<"\n\nERR: could not get terminal options\n\n";
}
else
{
ttable.c_cflag &= ~PARENB;
ttable.c_cflag &= ~CSTOPB;
ttable.c_cflag &= ~CSIZE;
ttable.c_cflag |= CS8;
ttable.c_cflag &= ~CRTSCTS;
ttable.c_cflag |= CREAD | CLOCAL;
ttable.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
ttable.c_oflag &= ~OPOST;
ttable.c_cc[VMIN] = 0;
ttable.c_cc[VTIME] = 0;
cfsetospeed(&ttable,9600);
if(tcsetattr(arduino,TCSANOW,&ttable)<0)
{
cout<<"\n\nERR: could not set new terminal options\n\n";
}
else
{
do
{
cout<<"\n\ninsert a number between 0 and 179";
cin>>angle;
arduino<<angle;
}while(angle<=179);
arduino.close();
}
}
}
}
It should connect to arduino , then ask me a number between 0 an 179 and the send that number to arduino which aplly that number as an angle to a servo motor;
But it stops at arduino.open("/dev/tty.usbmodem3a21") .What can i do ?

Answer 1

I think your problems appear in these lines of code
if(tcgetattr(arduino,&ttable)<0) {
// ...
}
else {
// ...
if(tcsetattr(arduino,TCSANOW,&ttable)<0) {
// ...
}
}
The arduino variable is of type ofstream, where tcgetattr() and tcsetattr() expect a file descriptor obtained with open() at this point.
ofstream provides an automatic conversion to bool and thus int implicitely. Supposed the
arduino.open("/dev/tty.usbmodem3a21");
went OK, you are effectively passing 1 to tcgetattr() and tcsetattr(), which is the standard input file descriptor.
Solution is not to use a ofstream for arduino, but an ordinary file descriptor
int arduino = open("/dev/tty.usbmodem3a21",O_WRONLY);