IOTAppStory::addField() crashes with heap variables

[tbaumann]

I have the feeling addField() somehow gets all confused if I use heap variables.

#define SENSIDX 2 // Number of sensors on bus - 1.
char* sensorNames[SENSIDX];
char* sensorLabels[SENSIDX];

  for(int index = 0; index <= SENSIDX; index++){
    sensorLabels[index] = (char*) malloc(15);
    sensorNames[index]  = (char*) malloc(16 + 1); // addField length parameter seems to be strlen not bytes

    sprintf(sensorLabels[index], "Sensor %d Name", index);
    strcpy(sensorNames[index], "Unnamed");

    IAS.addField(sensorNames[index], sensorLabels[index], 16, 'L');
  }

I suspect that the const for label is meant seriously?

Apart from the fact that I deeply dislike that solution. It also doesn't work. (Guru meditation)

const char* sensorLabels[] = {"Sensor 0", "Sensor 1", "Sensor 2"} ;

No mallocs and strcpy this time.

I'm no expert. But that looks const enough to me.

Is const char *fieldLabel indeed the problem here?

Can I perhaps mark it const and promise I won't change the value at runtime but initialise it dynamically?

[tbaumann]

  IAS.addField(sensorNames[0], "Sensor 0", 16, 'L');
  IAS.addField(sensorNames[1], "Sensor 1", 16, 'L');
  IAS.addField(sensorNames[2], "Sensor 2", 16, 'L');

Crashes equally. Const-ness of the label isn't even the problem here.

I'm quite confused now.

[Onno-Dirkzwager]

Hi @tbaumann, you are using this function in a way it was never intended for. But I get where you are comming from... as a programmer you do not want to repeat things... and rather setup a loop for this. We will definitely look into this.

For now you will have to use it like in the examples: char LEDpin = "2"; char blinkTime = "1000";

IAS.addField(LEDpin, "ledpin", 2, 'P'); IAS.addField(blinkTime, "Blinktime(mS)", 5, 'N');

So in your case: char sensorName0 = "Example 1"; char sensorName1 = "Example 2"; char* sensorName2 = "Example 3";

IAS.addField(sensorName0, "Sensor 0", 16, 'L'); IAS.addField(sensorName1, "Sensor 1", 16, 'L'); IAS.addField(sensorName2, "Sensor 2", 16, 'L');

(sensor name value, html field name, max char that can be saved from html, fieldtype)

[tbaumann]

Thanks Onno, I can certainly do it that way. No problem. The code repetition was in the end not really too bad. Perhaps I do it one day in preprocessor if I can actually be bothered.

Good to know I didn't just do something trivially wrong, thanks. I don't so C very often. 😄

[Onno-Dirkzwager]

Great, good luck with your projects! And if your question is answered please close this issue. (it's better for the stats if the issue opener closes it)