CMDmessenger library

Question

I am trying to use the CMDmessanger library on my Arduino uno, and am facing an issue.

My issue starts right from the ArduinoController.ino example.

When i send the frequency command

3,1;

The led starts blinking correctly, once per second.

But when I send a wrong command (basically a command without an argument)

3;

The led just stops blinking. The state of the led depends on which state it was in when I sent the command.

I realised that, when I send the wrongly formatted command, it takes the frequency as 0.

Is there any method by which I can make sure that the command is received in the right format, before it is executed? Ideally I would love it if there is a method to know how many arguments were received, and I could call the readBoolArg, or other equivalent functions to retrieve the argument data.

I am planning on using this library for quite a few projects, and I don't want to be in a situation where things went wrong because there was not formatting check.

Thanks in advance.

• Vinayak Shantaram Joshi: For some extra context, I am a developer at Inventrom Pvt Ltd and developing a library for interfacing the Bolt WiFi module with the Arduino Here is a link if anyone is interested.

Answer 1

The example code uses cmdMessenger.readFloatArg(); (source) to read an argument.

void OnSetLedFrequency()
{
 // Read led state argument, interpret string as boolean
 ledFrequency = cmdMessenger.readFloatArg();
 // Make sure the frequency is not zero (to prevent divide by zero)
 if (ledFrequency < 0.001) { ledFrequency = 0.001; }
 // translate frequency in on and off times in miliseconds
 intervalOn = (500.0/ledFrequency);
 intervalOff = (1000.0/ledFrequency);
 cmdMessenger.sendCmd(kAcknowledge,ledFrequency);
}

That function will set ArgOk to false if there was no next argument.

float CmdMessenger::readFloatArg()
{
 if (next()) {
 dumped = true;
 ArgOk = true;
 //return atof(current);
 return strtod(current, NULL);
 }
 ArgOk = false;
 return 0;
}

Thus you should try to use public function

bool isArgOk();
/**
 * Returns if the latest argument is well formed.
 */
bool CmdMessenger::isArgOk()
{
 return ArgOk;
}

of the CmdMessenger object (which will return ArgOk) to check if the read argument was okay. You could e.g. modify the code as follows

void OnSetLedFrequency()
{
 // Read led state argument, interpret string as boolean
 ledFrequency = cmdMessenger.readFloatArg();
 //Did we just read garbage because the argument wasn't there?
 if(!cmdMessenger.isArgOk()) {
 //Using Serial might be a bad idea because that cmdMessanger operates on the same Serial stream.. but you get the idea.
 Serial.println("You didn't supply a correct argument! Error.");
 return; //goodbye
 }
 // Make sure the frequency is not zero (to prevent divide by zero)
 if (ledFrequency < 0.001) { ledFrequency = 0.001; }
 // translate frequency in on and off times in miliseconds
 intervalOn = (500.0/ledFrequency);
 intervalOff = (1000.0/ledFrequency);
 cmdMessenger.sendCmd(kAcknowledge,ledFrequency);
}

• Vinayak Shantaram Joshi: Thank you. I didn't realise that's how the isArgOk function worked.