Issues with variable pointers

system · October 29, 2013, 10:05am

I'm making a UI for my AD9850 DDS with a standard 16x2 lcd screen and a 4x4 keypad. I have been having issues with variable pointers:

void screenBackspace(unsigned long &var) {
  var -= var % 10; // Remove last digit to prevent any division errors
  var /= 10; // Divide by ten
  lcd.setCursor(1,1);
  lcd.print("               "); // 15 spaces - clear bottom line (except for '>')
  lcd.setCursor(1,1);
  if (var != 0) {lcd.print(var);}
  keyHoldTimer.setInterval(1500);
  keyHoldTimer.reset();
  keyHoldTimer.enable();
}

void screenInput(unsigned long &var, KeypadEvent key) {
  int tkey = key - '0';
  var = var * 10;
  var = var + tkey;
  if (var > bwLimit) var = bwLimit; // Restrict bandwidth to pre-set limit
  lcd.setCursor(1,1);
  lcd.print(var);
  keyHoldTimer.setInterval(1500);
  keyHoldTimer.reset();
  keyHoldTimer.enable(); // Start key hold timer
}

void keyHold() {
  unsigned long *var;
  if (kpd.getState() == HOLD) {
    switch (currentScreen) {
      case s_staticFreq: {
        *var = &staticFreq;
        break;
      }
      
      case s_sweepFreqStart: {
        *var = &sweepFreqStart;
        break;
      }
      
      case s_sweepFreqEnd: {
        *var = &sweepFreqEnd;
        break;
      }
      
      case s_sweepStep: {
        *var = &sweepStep;
        break;
      }
    }
    
    switch (currentKey) {
      case '*': {
        screenBackspace(*var);
        break;
      }
      
      case '#':
      case 'A':
      case 'B':
      case 'C':
      case 'D': {
        keyHoldTimer.disable(); // Do nothing for non-numerical keys (apart from * which is backspace);
        break;
      }
      
      default: { // Number keys
        screenInput(*var, currentKey);
        break;
      }
    }
  }
  else {
    keyHoldTimer.disable();
  }
}

This is the bit I'm having trouble with. screenInput() and screenBackspace() work fine, but when compiling I get the following error message:
error: invalid conversion from 'long unsigned int*' to 'long unsigned int'
I have used this page as my reference.
Any ideas as to what is going wrong?

system · October 29, 2013, 10:13am

  unsigned long *var;

Every single use of this variable is as a variable, not a pointer. Why is var declared to be a pointer?

Any ideas as to what is going wrong?

There is a lot of code missing. Things that explain why you are storing addresses in variables, etc. The line number that generates the error is also missing.

system · October 29, 2013, 10:20am

The first line number is 132 - ‘*var = &staticFreq’.
I didn’t post the whole sketch because it’s quite big, but here you go:

#include <TimedAction.h>
#include <LiquidCrystal.h>
#include <Keypad.h>
#include <String.h>

const byte ROWS = 4;
const byte COLS = 4;
const String fversion = "v0.1";
const unsigned long bwLimit = 50000000;
const int lcdTimer = 1;
enum Screen {s_root, s_staticFreq, s_staticFreqOutput, s_sweepFreqStart, s_sweepFreqEnd, s_sweepStep};

char keys[ROWS][COLS] = {
  {'*', '0', '#', 'D'},
  {'7', '8', '9', 'C'},
  {'4', '5', '6', 'B'},
  {'1', '2', '3', 'A'} };
byte rowPins[ROWS] = {44, 45, 46, 47};
byte colPins[COLS] = {43, 42, 41, 40};
unsigned long staticFreq;
unsigned long sweepFreqStart;
unsigned long sweepFreqEnd;
unsigned long sweepStep;
Screen currentScreen = s_root;
int lcdScrollLength = 0;
String lcdStaticTopLine;
int lcdScrollDelay = 1000; // Delay while screen has reached either end of the scroll cycle
int lcdScrollLetterDelay = 150; // Delay between each letter
int lcdScrollStage = 0;
int lcdPositionCounter = 0;
boolean lcdPositionCounterSet = false;
int keyHoldDelay = 500; // When a key is held, numbers are input every keyHoldDelay milliseconds.

TimedAction lcdScrollTimer = TimedAction(lcdScrollDelay, lcdScrollEvent);
TimedAction keyHoldTimer = TimedAction(keyHoldDelay, keyHold);
LiquidCrystal lcd(22, 23, 24, 25, 26, 27);
Keypad kpd = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);
char currentKey;

void setup() {
  lcdScrollTimer.disable();
  keyHoldTimer.disable();
  kpd.addEventListener(updateScreen);
  kpd.setHoldTime(400);
  Serial.begin(9600);
  lcd.begin(16, 2);
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("AD9850 DDS");
  lcd.setCursor(0,1);
  lcd.print("Firmware ");
  lcd.print(fversion);
  delay(2000);
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("A: Static freq");
  lcd.setCursor(0,1);
  lcd.print("B: Sweep freqs");
}

void loop() {
  kpd.getKey();
  lcdScrollTimer.check();
  keyHoldTimer.check();
}

void lcdScrollEvent() {
  Serial.println("lcdScrollEvent called");
  switch (lcdScrollStage) {
    case 0: {
      if (!lcdPositionCounterSet) {
        lcdPositionCounter = 0;
        lcdPositionCounterSet = true;
      }
      if (lcdPositionCounter >= lcdScrollLength) {
        lcdScrollStage += 1;
        lcdScrollTimer.setInterval(lcdScrollDelay);
        break;
      }
      lcd.scrollDisplayLeft();
      lcd.setCursor(lcdPositionCounter + 1, 0);
      lcd.print(lcdStaticTopLine);
      lcdPositionCounter++;
      lcdScrollTimer.setInterval(lcdScrollLetterDelay); // TEH MAGIC!
      break;
    }
    
    case 1: {
      for (lcdPositionCounter = 0; lcdPositionCounter < lcdScrollLength; lcdPositionCounter++) {
        lcd.scrollDisplayRight();
      }
      lcdScrollStage -= 1;
      // Lcd scroll timer already set: no need to do so again here
      lcdPositionCounterSet = false;
      lcd.setCursor(0,0);
      lcd.print(lcdStaticTopLine);
      break;
    }
  }
}

void lcdScroll(int length, String topLine) {
  lcdScrollTimer.setInterval(lcdScrollDelay); // Reset interval
  lcdScrollTimer.reset(); // Reset timer
  lcdPositionCounter = 0; // Reset position
  lcdScrollLength = length;
  lcdStaticTopLine = topLine;
  lcdScrollTimer.enable();
}

void noLcdScroll() {
  lcdScrollTimer.disable();
}

void screenBackspace(unsigned long &var) {
  var -= var % 10; // Remove last digit to prevent any division errors
  var /= 10; // Divide by ten
  lcd.setCursor(1,1);
  lcd.print("               "); // 15 spaces - clear bottom line (except for '>')
  lcd.setCursor(1,1);
  if (var != 0) {lcd.print(var);}
  keyHoldTimer.setInterval(1500);
  keyHoldTimer.reset();
  keyHoldTimer.enable();
}

void keyHold() {
  unsigned long *var;
  if (kpd.getState() == HOLD) {
    switch (currentScreen) {
      case s_staticFreq: {
        *var = &staticFreq;
        break;
      }
      
      case s_sweepFreqStart: {
        *var = &sweepFreqStart;
        break;
      }
      
      case s_sweepFreqEnd: {
        *var = &sweepFreqEnd;
        break;
      }
      
      case s_sweepStep: {
        *var = &sweepStep;
        break;
      }
    }
    
    switch (currentKey) {
      case '*': {
        screenBackspace(*var);
        break;
      }
      
      case '#':
      case 'A':
      case 'B':
      case 'C':
      case 'D': {
        keyHoldTimer.disable(); // Do nothing for non-numerical keys (apart from * which is backspace);
        break;
      }
      
      default: { // Number keys
        screenInput(*var, currentKey);
        break;
      }
    }
  }
  else {
    keyHoldTimer.disable();
  }
}

void screenInput(unsigned long &var, KeypadEvent key) {
  int tkey = key - '0';
  var = var * 10;
  var = var + tkey;
  if (var > bwLimit) var = bwLimit; // Restrict bandwidth to pre-set limit
  lcd.setCursor(1,1);
  lcd.print(var);
  keyHoldTimer.setInterval(1500);
  keyHoldTimer.reset();
  keyHoldTimer.enable(); // Start key hold timer
}

void updateScreen(KeypadEvent key) {
  currentKey = key;
  
  if (kpd.getState() == PRESSED) {
    if (key == 'C') {
      noLcdScroll();
      lcd.clear();
      lcd.noBlink();
      lcd.setCursor(0,0);
      lcd.print("A: Static freq");
      lcd.setCursor(0,1);
      lcd.print("B: Sweep freqs");
      staticFreq = 0;
      sweepFreqStart = 0;
      sweepFreqEnd = 0;
      sweepStep = 0;
      currentScreen = s_root;
    }
    
    switch (currentScreen) {
      case s_root: {
        switch (key) {
          case 'A': {
            lcd.clear();
            lcd.setCursor(0,0);
            lcd.print("Enter frequency");
            lcd.setCursor(0,1);
            lcd.print(">");
            lcd.blink();
            currentScreen = s_staticFreq;
            break;
          }
          case 'B': {
            lcd.clear();
            lcd.setCursor(0,0);
            lcd.print("Enter start freq");
            lcd.setCursor(0,1);
            lcd.print(">");
            lcd.blink();
            currentScreen = s_sweepFreqStart;
            break;
          }
        }
        break;
      }
    
      case s_staticFreq: {
        switch (key) {
          case '*': {
            screenBackspace(staticFreq);
            break;
          }
          
          case '#': {
            if (staticFreq > 0) {
              lcd.noBlink();
              lcd.clear();
              lcd.setCursor(0,0);
              lcd.print("Beginning output");
              lcd.setCursor(0,1);
              lcd.print("Frequency(Hz): ");
              lcd.print(staticFreq);
              lcd.home();
              String scrollLen = String(staticFreq);
              lcdScroll(scrollLen.length() - 1, "Beginning output");            
              currentScreen = s_staticFreqOutput;
              
              // Set AD9850 module here
              
            }
            break;
          }
          
          case 'A':
          case 'B':
          case 'C':
          case 'D': {break;}
          
          default: {
            screenInput(staticFreq, key);
            break;
          }
        }
        break;
      }
      
      case s_sweepFreqStart: {
        switch (key) {
          case '*': {
            screenBackspace(sweepFreqStart);
            break;
          }
          
          case '#': {
            if (sweepFreqStart > 0) {
              lcd.clear();
              lcd.setCursor(0,0);
              lcd.print("Enter end freq");
              lcd.setCursor(0,1);
              lcd.print(">");
              lcd.blink();
              currentScreen = s_sweepFreqEnd;
            }
            break;
          }
          
          case 'A':
          case 'B':
          case 'C':
          case 'D': {break;}
          
          default: {
            screenInput(sweepFreqStart, key);
            break;
          }
        }
        break;
      }
    }
  }
}

system · October 29, 2013, 10:33am

  kpd.addEventListener(updateScreen);

So, when a key is pressed, you want updateScreen() to be called.

  kpd.getKey();

So, what's this useless code for? See if a key is pressed, but don't bother keeping that key. So, why bother?

void screenBackspace(unsigned long &var) {

Do you really want the value passed to this routine to be modified in the calling function?

void keyHold() {
  unsigned long *var;
        *var = &staticFreq;
         *var = &sweepFreqStart;
         *var = &sweepFreqEnd;
         *var = &sweepStep;

You are storing addresses in the memory location that var points to.

        screenBackspace(*var);

Then, you expect this function to divide the address by 10. How can you expect that to work?

var should not be a pointer, and screenBackspace() should not be a void function, and should not take a reference.

screenBackspace should be an unsigned long function, taking an unsigned long VALUE, and returning the modified value.

Then, keyHold() needs a complete rewrite.

system · October 29, 2013, 10:39am

kpd.getKey() is needed in the loop function because otherwise (for reasons beyond me) the event handler for keypresses doesn't get called. Thanks for your help, I will rewrite the functions + keyHold now.

system · October 29, 2013, 11:03am

Thanks, PaulS: it works well now
For anyone else who has the same (unlikely niche) problem, here is my code:

#include <TimedAction.h>
#include <LiquidCrystal.h>
#include <Keypad.h>
#include <String.h>

const byte ROWS = 4;
const byte COLS = 4;
const String fversion = "v0.1";
const unsigned long bwLimit = 50000000;
const int lcdTimer = 1;
enum Screen {s_root, s_staticFreq, s_staticFreqOutput, s_sweepFreqStart, s_sweepFreqEnd, s_sweepStep};

char keys[ROWS][COLS] = {
  {'*', '0', '#', 'D'},
  {'7', '8', '9', 'C'},
  {'4', '5', '6', 'B'},
  {'1', '2', '3', 'A'} };
byte rowPins[ROWS] = {44, 45, 46, 47};
byte colPins[COLS] = {43, 42, 41, 40};
unsigned long staticFreq;
unsigned long sweepFreqStart;
unsigned long sweepFreqEnd;
unsigned long sweepStep;
Screen currentScreen = s_root;
int lcdScrollLength = 0;
String lcdStaticTopLine;
int lcdScrollDelay = 1000; // Delay while screen has reached either end of the scroll cycle
int lcdScrollLetterDelay = 150; // Delay between each letter
int lcdScrollStage = 0;
int lcdPositionCounter = 0;
boolean lcdPositionCounterSet = false;
int keyHoldDelay = 200; // When a key is held, numbers are input every keyHoldDelay milliseconds.
int initialKeyHoldDelay = 1500; // Time you must hold a key before it will print several characters

TimedAction lcdScrollTimer = TimedAction(lcdScrollDelay, lcdScrollEvent);
TimedAction keyHoldTimer = TimedAction(initialKeyHoldDelay, keyHold);
LiquidCrystal lcd(22, 23, 24, 25, 26, 27);
Keypad kpd = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);
char currentKey;

void setup() {
  lcdScrollTimer.disable();
  keyHoldTimer.disable();
  kpd.addEventListener(updateScreen);
  kpd.setHoldTime(400);
  // Serial.begin(9600);
  // Debug only
  lcd.begin(16, 2);
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("AD9850 DDS");
  lcd.setCursor(0,1);
  lcd.print("Firmware ");
  lcd.print(fversion);
  delay(2000);
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("A: Static freq");
  lcd.setCursor(0,1);
  lcd.print("B: Sweep freqs");
}

void loop() {
  kpd.getKey();
  lcdScrollTimer.check();
  keyHoldTimer.check();
}

void lcdScrollEvent() {
  Serial.println("lcdScrollEvent called");
  switch (lcdScrollStage) {
    case 0: {
      if (!lcdPositionCounterSet) {
        lcdPositionCounter = 0;
        lcdPositionCounterSet = true;
      }
      if (lcdPositionCounter >= lcdScrollLength) {
        lcdScrollStage += 1;
        lcdScrollTimer.setInterval(lcdScrollDelay);
        break;
      }
      lcd.scrollDisplayLeft();
      lcd.setCursor(lcdPositionCounter + 1, 0);
      lcd.print(lcdStaticTopLine);
      lcdPositionCounter++;
      lcdScrollTimer.setInterval(lcdScrollLetterDelay); // TEH MAGIC!
      break;
    }
    
    case 1: {
      for (lcdPositionCounter = 0; lcdPositionCounter < lcdScrollLength; lcdPositionCounter++) {
        lcd.scrollDisplayRight();
      }
      lcdScrollStage -= 1;
      // Lcd scroll timer already set: no need to do so again here
      lcdPositionCounterSet = false;
      lcd.setCursor(0,0);
      lcd.print(lcdStaticTopLine);
      break;
    }
  }
}

void lcdScroll(int length, String topLine) {
  lcdScrollTimer.setInterval(lcdScrollDelay); // Reset interval
  lcdScrollTimer.reset(); // Reset timer
  lcdPositionCounter = 0; // Reset position
  lcdScrollLength = length;
  lcdStaticTopLine = topLine;
  lcdScrollTimer.enable();
}

void noLcdScroll() {
  lcdScrollTimer.disable();
}

unsigned long screenInput(unsigned long var, KeypadEvent key) {
  int tkey = key - '0';
  var = var * 10;
  var = var + tkey;
  if (var > bwLimit) var = bwLimit; // Restrict bandwidth to pre-set limit
  lcd.setCursor(1,1);
  lcd.print(var);
  keyHoldTimer.reset();
  keyHoldTimer.enable(); // Start key hold timer
  return var;
}

unsigned long screenBackspace(unsigned long var) {
  var -= var % 10; // Remove last digit to prevent any division errors
  var /= 10; // Divide by ten
  lcd.setCursor(1,1);
  lcd.print("               "); // 15 spaces - clear bottom line (except for '>')
  lcd.setCursor(1,1);
  if (var != 0) {lcd.print(var);}
  keyHoldTimer.reset();
  keyHoldTimer.enable();
  return var;
}

void keyHold() { 
  keyHoldTimer.setInterval(keyHoldDelay);
  unsigned long var;
  if (kpd.getState() == HOLD) {
    switch (currentKey) {
      case '*': {
        switch (currentScreen) {
          case s_staticFreq: {
            staticFreq = screenBackspace(staticFreq);
            break;
          }
          case s_sweepFreqStart: {
            sweepFreqStart = screenBackspace(sweepFreqStart);
            break;
          }
          case s_sweepFreqEnd: {
            sweepFreqEnd = screenBackspace(sweepFreqEnd);
            break;
          }
          case s_sweepStep: {
            sweepStep = screenBackspace(sweepStep);
            break;
          }
        }
        break;
      }
      
      case '#':
      case 'A':
      case 'B':
      case 'C':
      case 'D': {
        keyHoldTimer.disable(); // Cancel timer for non-numerical keys (apart from * which is backspace) otherwise it would continue indefinitely
        break;
      }
      
      default: { // Number keys
        switch (currentScreen) {
          case s_staticFreq: {
            staticFreq = screenInput(staticFreq, currentKey);
            break;
          }
          case s_sweepFreqStart: {
            sweepFreqStart = screenInput(sweepFreqStart, currentKey);
            break;
          }
          case s_sweepFreqEnd: {
            sweepFreqEnd = screenInput(sweepFreqEnd, currentKey);
            break;
          }
          case s_sweepStep: {
            sweepStep = screenInput(sweepStep, currentKey);
            break;
          }
        }
        break;
      }
    }
  }
  else {
    keyHoldTimer.disable();
    keyHoldTimer.setInterval(initialKeyHoldDelay);
  }
}

void updateScreen(KeypadEvent key) {
  currentKey = key;
  
  if (kpd.getState() == PRESSED) {
    if (key == 'C') {
      noLcdScroll();
      lcd.clear();
      lcd.noBlink();
      lcd.setCursor(0,0);
      lcd.print("A: Static freq");
      lcd.setCursor(0,1);
      lcd.print("B: Sweep freqs");
      staticFreq = 0;
      sweepFreqStart = 0;
      sweepFreqEnd = 0;
      sweepStep = 0;
      currentScreen = s_root;
    }
    
    switch (currentScreen) {
      case s_root: {
        switch (key) {
          case 'A': {
            lcd.clear();
            lcd.setCursor(0,0);
            lcd.print("Enter frequency");
            lcd.setCursor(0,1);
            lcd.print(">");
            lcd.blink();
            currentScreen = s_staticFreq;
            break;
          }
          case 'B': {
            lcd.clear();
            lcd.setCursor(0,0);
            lcd.print("Enter start freq");
            lcd.setCursor(0,1);
            lcd.print(">");
            lcd.blink();
            currentScreen = s_sweepFreqStart;
            break;
          }
        }
        break;
      }
    
      case s_staticFreq: {
        switch (key) {
          case '*': {
            staticFreq = screenBackspace(staticFreq);
            break;
          }
          
          case '#': {
            if (staticFreq > 0) {
              lcd.noBlink();
              lcd.clear();
              lcd.setCursor(0,0);
              lcd.print("Beginning output");
              lcd.setCursor(0,1);
              lcd.print("Frequency(Hz): ");
              lcd.print(staticFreq);
              lcd.home();
              String scrollLen = String(staticFreq);
              lcdScroll(scrollLen.length() - 1, "Beginning output");            
              currentScreen = s_staticFreqOutput;
              
              // Set AD9850 module here
              
            }
            break;
          }
          
          case 'A':
          case 'B':
          case 'C':
          case 'D': {break;}
          
          default: {
            staticFreq = screenInput(staticFreq, key);
            break;
          }
        }
        break;
      }
      
      case s_sweepFreqStart: {
        switch (key) {
          case '*': {
            sweepFreqStart = screenBackspace(sweepFreqStart);
            break;
          }
          
          case '#': {
            if (sweepFreqStart > 0) {
              lcd.clear();
              lcd.setCursor(0,0);
              lcd.print("Enter end freq");
              lcd.setCursor(0,1);
              lcd.print(">");
              lcd.blink();
              currentScreen = s_sweepFreqEnd;
            }
            break;
          }
          
          case 'A':
          case 'B':
          case 'C':
          case 'D': {break;}
          
          default: {
            sweepFreqStart = screenInput(sweepFreqStart, key);
            break;
          }
        }
        break;
      }
    }
  }
}

system · May 5, 2021, 8:23pm