Running LORA.receive(str) timeout extension using loop error

[Bambofy]

Hi,

I'm trying to extend the timeout for the receive function by putting it in a for loop. It can receive the first message fine, but in the next loops, it receives garbage?

Receiver

int state = 0;
String str = "";
for (int i = 0; i < 10; i++)
{
    state = LORA.receive(str);
    if (state == ERR_NONE)
    {
         Serial.println(str);
     }
}

Transmitter

void loop()
{
    int state = LORA.transmit("hello world!");
    if (state == ERR_NONE) Serial.println("Success");
}

Thanks, Richard

[jgromes]

In your for loop, you're storing the received data using a String variable that was created outside of the for loop. String class allocates memory dynamically, hence unpredictable stuff will happen when it's used in such a way.

The issue will disappear (sort of) if you move the declaration into the for loop, i.e.

int state = 0;
for (int i = 0; i < 10; i++)
{
    String str = "";
    state = LORA.receive(str);
    if (state == ERR_NONE)
    {
         Serial.println(str);
     }
}

From memory point of view however, this is even worse, since RAM will now fragment quickly - I would expect the MCU to reset every few seconds.

Why are you using String class in the first place?

[jgromes]

If what you're trying to achieve is longer time in receive mode, I sugggest you use interrupt-driven methods - see ReceiveInterrupt example for details.

[Bambofy]

Thanks, moving the String object into the loop solved the memory issue. I'm really not sure what the problem is with the dynamically allocated String object? If i do this:

String str = "";
int counter = 0;
function()
{
   str = String(counter);
   counter++;
}

doesn't the string object get deallocated? also what's the best replacement for this because i rely heavily on the string object functions?

thanks, Richard

[jgromes]

Where would it get deallocated? Looking at the String implementation, all the contructor does is it sets the buffer pointer to null, that doesn't mean the dynamic buffer is deallocated - it means it's now inaccessible and leaking memory. Sort of like doing this:

char* p = new char[10];
p = new char[5]; // 10 bytes are now inaccessible
delete[] p; // only 5 bytes can be deallocated

Arduino String is notorious for causing all kinds of memory issues - I try to avoid it at all costs. Especially for your application, if dynamic memory allocation is necessary (e.g. for receiving data), I would strongly suggest taking good care of proper memory management and only using C-strings.

[Bambofy]

Wow that is really bad memory management! i will convert my String objects now.