iterate through values in an array of strings to print

Question

I (think I) am trying to iterate through the values of an array and print the string to a tft. I have declared the array of 4 strings, and that works fine. But when I try to print it, I get garbage. Am I missing a nuance of print? Or do I just not understand how to use arrays and strings...?

The code is as follows:

Declarations:

//Active System
char hvacSystems[4][5] = {"Off", "Fan", "Cool", "Heat"};
int activeSystem = 0;  
String displayActiveSystem = hvacSystems[activeSystem]; <-- Should now be String "off"

Use (note the fake if statement for the question)

  if(systemNeedsToBeCycled){
    activeSystem++;
    displayActiveSystem = hvacSystems[activeSystem]; <-- Should now be String "Fan"
    tft.print(displayActiveSystem);
  }

Instead I get random characters most of the time, sometimes nothing.

In case its a memory thing, please know that:

Sketch uses 26,480 bytes (92%) of program storage space. Maximum is 28,672 bytes. Global variables use 1,126 bytes (43%) of dynamic memory, leaving 1,434 bytes for local variables. Maximum is 2,560 bytes.

Answer 1

If the variable activeSystem exceeds the length of the array, it's out of bounds, at which point the behavior is undefined.
In your case you get "garbage data", which is actually just data in memory after the array.

Because the is no implicit check for array bounds, you need to check them yourself.

Answer 2

I think this is the correct way to create an array of C strings:

    char * hvacSystems[] = {"Off", "Fan", "Cool", "Heat"};
    int activeSystem = 0;  
    char * displayActiveSystem = hvacSystems[activeSystem]; 

    if(systemNeedsToBeCycled){
        activeSystem++;    // make sure to set a bound for this variable
        displayActiveSystem = hvacSystems[activeSystem]; 
        tft.print(displayActiveSystem);
    }

Since strings are basically stored as char pointers so an array of strings is an array of char * variables. Or you could create an array of Arduino strings:

    String hvacSystems[] = {"Off", "Fan", "Cool", "Heat"};
    int activeSystem = 0;  
    String displayActiveSystem = hvacSystems[activeSystem]; 

    if(systemNeedsToBeCycled){
        activeSystem++;    // make sure to set a bound for this variable
        displayActiveSystem = hvacSystems[activeSystem]; 
        tft.print(displayActiveSystem);
    }

Answer 3

I am not sure I understand 100% but here is my best shot. If the below is wrong the issue is not due to being out of memory. Try this

//Active System
char hvacSystems[] = {"Off", "Fan", "Cool", "Heat"}; 
// or char hvacSystems[4] = {"Off", "Fan", "Cool", "Heat"}
int activeSystem = 0;  
String displayActiveSystem = hvacSystems[activeSystem]; <-- Should now be String "off"

if(systemNeedsToBeCycled){
    activeSystem++;
    displayActiveSystem = hvacSystems[activeSystem]; <-- Should now be String "Fan"
    tft.print(displayActiveSystem);
}

Your line

char hvacSystems[4][5] = {"Off", "Fan", "Cool", "Heat"};

You are attempting to create a two dimensional array here. Essentially a 4x5 table. With your code if you do

tft.print(hvacSystems[0][1]);

It should give you "Off". Basically you made a table that looks like

0{"Off", "Fan", "Cool", "Heat", null}

1{null, null, null, null, null}

2{null, null, null, null, null}

3{null, null, null, null, null }

Arrays: https://www.arduino.cc/en/Reference/Array 2d Arrays:

http://forum.arduino.cc/index.php?topic=220385.0

Answer 4

The problem does not appear to be what you think it is, because I can't reproduce it.

See this:

//Active System
char hvacSystems[4][5] = {"Off", "Fan", "Cool", "Heat"};
int activeSystem = 0;  

String displayActiveSystem;

bool systemNeedsToBeCycled = true;

void setup ()
  {
  Serial.begin (115200);
  Serial.println ();

  displayActiveSystem = hvacSystems[activeSystem]; // <-- Should now be String "off"

  Serial.println (displayActiveSystem);

  if(systemNeedsToBeCycled){
    activeSystem++;
    displayActiveSystem = hvacSystems[activeSystem]; // <-- Should now be String "Fan"
    Serial.println (displayActiveSystem);
    }
  }  // end of setup

void loop ()
  {

  }  // end of loop

Output:

Off
Fan

Please post a complete sketch that reproduces the problem. The placement of variables, and their type, might influence the result.

I used Serial.println() to show the variable contents, which are what you expected.

---

Possibly this will work better:

tft.print(displayActiveSystem.c_str ());