Thread: Send strings to port in Linux

One subject for this is probably enough - so I'd suggest that the moderators delete the other one.

Exactly what happens? Does it give an error message, or simply fails to do what you expect?

If it's a USB modem, are you sure that it will at all respond to simple text packets like that, and that is doesn't have a protocol on that emulates the serial interface?

--
Mats

Hi Mats,

The program runs ok, no errors generated by the compiler. It seems to just fail in opening the connection to the port located at /dev/ttyUSB1. It skips straight to the else and prints Unsuccessful to the console. This is my first time programming for Linux, so I was just wondering if I had done anything wrong.

I just presumed it accepted text packets and I'm not sure if there are any protocols on it. I'll look into it.

I did change the code slightly (shown below).

Code:

#include <stdio.h>
#include <iostream>
#include <fstream>
#include <string>
#include <stdlib.h>
#include <time.h>

using namespace std;

#define MODEL_ID "at+gmm"

int main (){
	
	string result;
	fstream USB1;
	
	USB1.open ("/dev/ttyUSB1", fstream::in | fstream::out);
	
	if (USB1.is_open()){
		cout << "Successfully opened communications to Modem" << endl;
		USB1 << MODEL_ID;
		cout << "Sending command... " << MODEL_ID << endl;
		USB1 >> result;
		USB1.close();
		cout << "Received the following back: " << result << endl;
		}
	else {
		cout << "Unsuccessful" << endl;
		}
}

Thanks for the suggestion

Brownie

you may want to try printing errno in the case of "unsuccesful" - I presume you have rights to open that file (e.g. you are running the program under root priviliges)?

To check that the file can be opened at all, you could do something like "cat /dev/ttyUSB1" or "cat > /dev/ttyUSB1".

You could also try using miniterm (I think that's the name of it), which is a terminal emulator for Linux - sort of like Hyperterminal (but not at all like it in most respects).

--
Mats

Why are you opening the device twice? Open it once, in read/write mode.

Originally Posted by brewbuck

Why are you opening the device twice? Open it once, in read/write mode.

Which the second posted code does, right?

--
Mats