passing pointers to an array of bytes

Using Arduino Programming Questions
#1

i’ve been working in C# and have totally forgotten how to use pointers (to my chagrin … and frustration)

i’m passing an array of pointers of bytes to a function and the receiving function does not know their values.

here’s a code sample

String getString_WorkOut_Time(byte *bytTime[3])
{
  String strHours = String(*bytTime[0]);
  while (strHours.length() < 2)
    strHours = "0" + strHours;
  
  String strMinutes = String(*bytTime [1]);
  while (strMinutes.length() < 2)
    strMinutes = "0" + strMinutes;

  String strSeconds = String(*bytTime[2]);
  while (strSeconds.length() < 2)
    strSeconds = "0" + strSeconds;

  // /*
  Serial.print(F("EditWorkOut_Time_Draw() "));
  Serial.print(strHours);
  Serial.print(F(":"));
  Serial.print(strMinutes);
  Serial.print(F(":"));
  Serial.println(strSeconds);
  // */


  String strTime = strHours + ":" + strMinutes + ":" + strSeconds;
  return strTime;
}

bool EditWorkOut_Time()
{
  Serial.print(F("EditWorkOut_Time()-> before call:"));
  Serial.print(String(cWorkout.bytTimer_Hours));
  Serial.print(F(":"));
  Serial.print(String(cWorkout.bytTimer_Minutes));
  Serial.print(F(":"));
  Serial.println(String(cWorkout.bytTimer_Seconds));
  int intRange[] = {99, 60, 60};
  byte *bytTime[3] = { cWorkout.bytTimer_Hours, cWorkout.bytTimer_Minutes, cWorkout.bytTimer_Seconds};
  
  getString_WorkOut_Time(bytTime);
  
  Serial.print(F("EditWorkOut_Time()-> after call :"));
  Serial.print(String(cWorkout.bytTimer_Hours));
  Serial.print(F(":"));
  Serial.print(String(cWorkout.bytTimer_Minutes));
  Serial.print(F(":"));
  Serial.println(String(cWorkout.bytTimer_Seconds));


  return;
  }

the results on my Serial port are

EditWorkOut_Time()-> before call:1:30:12
Hours before adding 0s000Hours after adding 0s
EditWorkOut_Time_Draw() 00:30:00
EditWorkOut_Time()-> after call :1:30:12

clearly the values of h:m:s being sent are 1:30:12
but the receiving function thinks they’re 0:30:00 ?!?

the example I’m following is from C - Array of pointers - Tutorialspoint
even though the example is not passing the pointers am i not using them the same way?

Live Demo
#include <stdio.h>
 
const int MAX = 3;
 
int main () {

   int  var[] = {10, 100, 200};
   int i, *ptr[MAX];
 
   for ( i = 0; i < MAX; i++) {
      ptr[i] = &var[i]; /* assign the address of integer. */
   }
   
   for ( i = 0; i < MAX; i++) {
      printf("Value of var[%d] = %d\n", i, *ptr[i] );
   }
   
   return 0;
}
#2

It’s hard to know, but in this snippet:

 byte *bytTime[3] = { cWorkout.bytTimer_Hours, cWorkout.bytTimer_Minutes, cWorkout.bytTimer_Seconds};

I don’t see any reason to suppose that those three things are pointers, I’d expect that they’re just bytes.

#3

I assume cWorkout is a struct?
to set up aan array pointers use the & (address of) operator

byte *bytTime[3] = { &cWorkout.bytTimer_Hours, &cWorkout.bytTimer_Minutes, &cWorkout.bytTimer_Seconds};
#4

You are setting your pointers to values, not addresses

byte *bytTime[3] = { cWorkout.bytTimer_Hours, cWorkout.bytTimer_Minutes, cWorkout.bytTimer_Seconds};

This seems overly complicated. Why not pass the entire cWorkout object by reference and then manipulate the fields directly?

#5

thank you for your reply.
I actually figured out the & addressing needed …
but I’ll take your idea about passing the entire class by reference as well.

happy Quararduino Day

#6