Serial monitor problem when using strcat

Projects Programming
1

Hi,
I am working with an Arduino Uno clone to read temperature of two RTC sensors. For this, I have created my own library NTC_3950_10k.h, which is just a simple interface to convert and parse the temperature read by the sensor.

My problem is that "mysteriously" two more lines on my loop function containing calls to strcat completely halts the processor and makes the

Here my code:

TemperatureReaderStandalone.ino

#include "NTC_3950_10k.h"

unsigned int inByte = 0;
NTC_3950_10k *tempSensor, *tempSensor2;
char telemetry[10];
void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  tempSensor = new NTC_3950_10k(A0);
  tempSensor2 = new NTC_3950_10k(A1);
  memset(telemetry, 0, sizeof(telemetry));
  
  //pinMode(A0, INPUT);
  while(!Serial);
  Serial.print("pin on tempsensor1 "); // <---- EXECUTION STOPS HERE
  Serial.println(tempSensor->pin);
}

void loop() {
  
  memset(telemetry, 0, sizeof(telemetry));
  strcat(telemetry,tempSensor->readTemperatureStr());
  strcat(telemetry,"\t");
  strcat(telemetry,tempSensor2->readTemperatureStr());
  Serial.println(telemetry);
  
  delay(100);
}

NTC_3950_10k.cpp

#include "NTC_3950_10k.h"
#include <math.h>
#include <Arduino.h>

float NTC_3950_10k::raw2celsius(unsigned int x){
  return 5.5437465781E-16*pow(x,6) - 2.2822487822E-13*pow(x,5) - 1.5520552248E-9*pow(x,4) + 2.2362994944E-06*pow(x,3) - 1.2423493602E-03*pow(x,2) + 4.0356315840E-01*x - 5.1354957493E+01;
}

NTC_3950_10k::NTC_3950_10k(int pin){
  this->pin = pin;  
  pinMode(pin, INPUT);
}

float NTC_3950_10k::readTemperature(){
  return raw2celsius(analogRead(pin));
}

char* NTC_3950_10k::readTemperatureStr(){
  float temp = raw2celsius(analogRead(pin));
  dtostrf(temp, 6, 2, lastReadTemperature);
  return lastReadTemperature;
}

NTC_3950_10k.h

class NTC_3950_10k {
  public:
    NTC_3950_10k(int);
    float readTemperature();
    char* readTemperatureStr();
    char lastReadTemperature[6];
    int pin;
  private:
    float raw2celsius(unsigned int x);
};

Serial Monitor output:

03:04:36.572 -> pin on tempsensor1 14
03:04:36.758 -> pin⸮⸮⸮ pi⸮⸮⸮⸮⸮pin

The funny thing is that if I comment the line 25, strcat(telemetry,tempSensor2->readTemperatureStr());, the Arduino runs perfectly: it prints the message on the setup() and continues gracefully to the loop() by printing the temperature. I have my suspicion on the way memory is handled but I do not know how to explain this behaviour.

2

This can hold 9 ASCII characters. How many are you trying to stuff into it?

Use strncat() to prevent buffer overflow, overwriting memory and causing program malfunctions.

3

Thanks for the prompt answer. Yes, the problem is solved by making the telemetry variable bigger (10 -> 15).

A follow up question: in case I am working in a bigger project, is there any way to visualise this on the final object file or I should just be careful on the code? Is there some analysis tool or method I can use to troubleshoot these things?

4

You should be very careful with the code, and use the n versions of the C-string handling routines, e.g. strncat(), snprintf(), strncpy(), etc.

Visualize ASCII character strings by printing them on the serial monitor, or any other serial terminal program.

1 Like
5

strlcat() is better.

1 Like
6

Even though it's not standard?

7

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