LinuxQuestions.org - Writing/reading to a modem via serial device?

I have a CDMA modem connected to an embedded system via USB. The driver for this device creates a device file at /dev/ttyUSB2. I wish to send AT commands to the modem and read the result returned by the modem. Minicom works for doing this, but I need to do this in an application. I wrote the following C++ code to test that this works:

Code:

//----------------------------------------------------------------------------

// Simple app for testing sending/receiving AT commands from a port

//----------------------------------------------------------------------------



#include <cstdio>

#include <iostream>

#include <string>



#define G_DEVICE_NAME "/dev/ttyUSB2"



FILE* G_deviceFile = NULL;



void SendCommand(const char* command, int length) {

        fwrite(command, 1, length, G_deviceFile);

}



char* ReadResult() {

        static char buffer[100];

        fread(buffer, 1, 100, G_deviceFile);

        return buffer;

}



using namespace std;



int main() {

        string commandOne = "ATZ";

        string commandTwo = "AT^SYSINFO";

        string commandThree = "AT+VROM?";



        G_deviceFile = fopen(G_DEVICE_NAME, "w+");

        if (G_deviceFile == NULL) {

                cout << "ERROR: could not open file: " << G_DEVICE_NAME << endl;

                return 1;

        }



        cout << "SENT: " << commandOne << endl;

        SendCommand(commandOne.c_str(), commandOne.size());

        cout << "RECV: " << ReadResult() << endl;



        cout << "SENT: " << commandTwo << endl;

        SendCommand(commandTwo.c_str(), commandTwo.size());

        cout << "RECV: " << ReadResult() << endl;



        cout << "SENT: " << commandThree << endl;

        SendCommand(commandThree.c_str(), commandThree.size());

        cout << "RECV: " << ReadResult() << endl;



        fclose(G_deviceFile);

        return 0;

}

However running this simple application managed to crash the entire system. :doh: I'm not sure if the problem is with my application or with the driver for this device, as the manufacturer of the modem is...well, they don't give me a lot of confidence in their product. I can't seem to capture the crash report either (doesn't show up in the syslog).

So I was wondering if I am way off base here with this sample code (i.e., this is not the way you want to write/read AT commands to the modem). Thanks for any input you can give.