Problem with c/c++ program - pointers/references

Here's a snippet of a program I've written:

int8_t extractParameters(struct scpi_token* command, bool parmsRequired, uint8_t minCount, uint8_t maxCount, struct scpi_token* param1, struct scpi_token* param2, struct scpi_token* param3) {
  struct scpi_token* args;
  args = command;
  while(args != NULL && args->type == 0) { // Ignore the parsed command token to leave args pointing at the first parameter
    args = args->next;
  }

  int8_t count = 0;
  while(args != NULL && args->type == 1) { // Then grab the actual parameters
    if (count == 0)
      param1 = args;
    if (count == 1) 
      param2 = args; 
    if (count == 3)
      param3 = args;
    count++;
    args = args->next;
  }
//  Serial.print(param2->value);

  // If paramaters aren't required and none passed, then ok
  if (count == 0 && !parmsRequired) 
    return count;


  if (count < minCount) { 
    scpi_error error;
    error.id = -109;
    error.description = "Missing Parameter Error; too few parameters passed";
    error.length = 50;
    scpi_queue_error(&ctx, error);
    return -1;
  }
  if (count > maxCount) {
    scpi_error error;
    error.id = -108;
    error.description = "Parameter not allowed; too many parameters passed";
    error.length = 49;
    scpi_queue_error(&ctx, error);
    return -1;    
  }
  return count;
}
scpi_error_t measureVoltage(struct scpi_parser_context* context, struct scpi_token* command){
//  struct scpi_token* args;
  struct scpi_token* expectedValue;
  struct scpi_token* resolution;
  float voltage;
  String unit;
  float divisor = 0.0;


  int8_t count = extractParameters(command, false, 2, 2, expectedValue, resolution, NULL);
  if (count != -1) {  
    if (count == 0 || (count == 2 && resolution->length == 1 && memcmp(resolution->value, "V", resolution->length) == 0)) {
      divisor = 1000.0;
      unit = "V";
    } else {
        if (count == 2 && (resolution->length == 2 && memcmp(resolution->value, "mV", resolution->length) == 0)) {
          divisor = 1.0;
          unit = "mV";
        } else {
            // SCPI ERROR        
            scpi_error error;
            error.id = -224;
            error.description = "Illegal Parameter Error;Invalid resolution";
            error.length = 42;
            scpi_queue_error(&ctx, error);
        }
    }
  }
  if (divisor > 0) {
    voltage = ( (rand() % (30000 + 1 - 0)) + 0) / divisor;
    Serial.print("Voltage is: ");
    Serial.print(voltage,3);
    Serial.println(unit);
  }
  scpi_free_tokens(command);
  return SCPI_SUCCESS;
}

It's actually a bit of SCPI processing code but what it does, is not relevant to my question, but here's the problem.  As the code stands above it doesn't work but if I uncomment this line:

//  Serial.print(param2->value);

in the first function under the while{} loop - line 19 - it does.  It compiles, but on line 53 I call the first function, expecting 'resolution' to have the value of 'param2' on return from the first function.  With the line uncommented, it does; with it commented it doesn't.

I'm assuming the compiler is tidying stuff up - perhaps it thinks param2 isn't used given that it isn't referenced in that function once set.  So, I further suspect that I'm not passing declaring the function correctly, or passing the parameters correctly.  I've scratched my head for a few hours now but I can't work out the issue - c/c++ is not a language I'm overly familiar with.

Can anyone help me work out what is going on?

Thanks

Andrew