send CTRL-Z through C++ program

Question

I am trying to write a simple C++ program that sends an SMS message out based on its input from the user. The simple C++ program fails to do the job:

#include<stdio.h>
#include <stdlib.h>     /* system, NULL, EXIT_FAILURE */

#include<iostream>
#define CTRL(x) (#x[0]-'a'+1)

using namespace std;
int main()
{
    char buffer[128];
    sprintf(buffer, "/opt/modemcli AT+CMGC=\"+112345678\"\rTEST%c", CTRL(z));
    printf (buffer);
    system(buffer);
    return 0;
}

modemcli is just a simple C++ program that writes messages to the USB port and reads the response.

modemcli is simple, here is a test:
/opt/modemcli AT
Received AT
OK

My guess is CMGC is not formed properly. The format is:

AT+CMGC="PHONE_NUMBER"<CR>SMS MESSAGE BODY.<Ctrl+z>

Can someone please help me figure this out?

I changed it to: AT+CMGC="+112345678"\013TESTTEST\026 but still isn't really working the right way. Any ideas? — user7459730, Mar 29 '17 at 22:39
@user7459730 Are you aware that `\013` and `\026` are interpreted as octal numbers? (They still would even without the `0` in the beginning.) https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences — Melebius, Aug 15 '17 at 13:01

score 1 · Accepted Answer · edited May 23 '17 at 12:09

First of all, I think you want to use the AT+CMGS command, not AT+CMGC. Check out the description of each command in 27.005 to see if you really want AT+CMGC. But before reading that document, read all of chapter 5 in V.250, that will teach you all the basics for AT command handling you need.

What you are attempting is impossible to do by using a generic command line program for sending AT command like modemcli or my atinout program. In order to run AT+CMGS on a modem, the program issuing it must have explicitly support for this specific AT command's behaviour.

This is because the need to wait for the "ready to receive" prompt from the modem before sending the payload. See the first part of this answer for details.

I have started working on a companion program to atinout specifically to handle AT+CMGS, but it is not done yet and do not hold your breath, the development is currently on hold.

send CTRL-Z through C++ program

1 Answers1