Two dimmensional array using pointers on Arduino Due

Vaclav_

I am trying to build a two dimmensional array - accessing LCD of 10 rows and 20 columns and be able to pass the pointer(s) to a function.
The function / method is declared in class and so is the pointer:

boolean DisplayImage(int \*\*Display);
int \*\*Display;

And the function:

boolean CImage::DisplayImage(int **Display)
{

#ifdef DEBUG
TRACE("CImage::DisplayImage ** ", 1);
#endif

int i, j, iRow, iCol;
iRow = 10;
iCol = 20;
int iCount = 0;

for ( i = 0; i < iRow; i++) {
for (j = 0; j < iCol; j++) {
lcd_i2c.clear();
lcd_i2c.print("location ");
lcd_i2c.setCursor(0, 1);
lcd_i2c.print("row i ");
lcd_i2c.print(i );
lcd_i2c.print(" col j ");
lcd_i2c.print(j );
lcd_i2c.setCursor(0, 2);
lcd_i2c.print("Display ");
**Display = iCount++; // set test value - works
lcd_i2c.print(**Display); // display is OK
// lcd_i2c.setCursor(0, 3);
// lcd_i2c.print("mask center ");
// lcd_i2c.print(**image );
**Display++;
delay(500);
}
}

return true;
}

Here is how I initialize the array

CImage::CImage (void)
{
// initialize array using pointers
// int **Display;
Display = new int *[10]; // display rows
for (int i = 0; i < 20; i++)
Display[i] = new int[10]; // display columns

}

Here are my questions: 1. I need some explanation about this syntax "Display = new int *[10]" - is the "Display " the variable name ? 2. I may have the rows / columns reversed because I really do not understand how is the array initialized.( That is my main question - I can take it from there ). 3. Unfortunatelly the example I got this from had 10 by 10 array so I am lost as far as what are the columns and what are the rows. 4. I use rows and columns because that is the underlying hardware and I understand it is irrelevant as far as multidimmensioal array goes. 5. Under present initialization I cannot get the LCD print pass first "row". The processor just stops ( Arduino Due). I would expect it to keep printing even if I runs out of valid pointer, but that is not the case. I sure would like to know why. ( It "runs" GCC compiler). Thank you for your time and help. Appreciate it. Cheers Vaclav PS I do not have a real debugger and using the LCD as "trace / debug "

Albert Holguin

Vaclav_Sal wrote:

1. I need some explanation about this syntax "Display = new int *[10]" - is the "Display " the variable name ?

Yes

Vaclav_Sal wrote:

2. I may have the rows / columns reversed because I really do not understand how is the array initialized.( That is my main question - I can take it from there ).

This is actually a matter of how the array is used (i.e. however you define it, or if you're using someone else's code, how they define it) since it's not really a matrix.

Vaclav_Sal wrote:

3. Unfortunatelly the example I got this from had 10 by 10 array so I am lost as far as what are the columns and what are the rows.

Without looking at the code, your guess is as good as mine... :)

Vaclav_Sal wrote:

5. Under present initialization I cannot get the LCD print pass first "row". The processor just stops ( Arduino Due). I would expect it to keep printing even if I runs out of valid pointer, but that is not the case. I sure would like to know why. ( It "runs" GCC compiler).

Does it say anything when it stops? ...is it crashing?

Vaclav_

It basically stops here lcd_i2c.print(**Display); // display is OK So it may be the LCD problem. If it crashed it should restart, but there is something different is Due (SAM) code from AVR code on start up, so it my be just stuck. I think I am assigning the values to the wrong pointer after the first array is done. I actually should use plain array and not pointers since I need to do convolution with 3x3 matrix to detect edge. I am not sure this is correct - the function gets a double pointer and than I assign to double pointer. But if I assign Display = iCount the compiler does not like it and I am still learning how to "translate" compiler / Arduino error messages.

    lcd\_i2c.setCursor(0, 2);
     lcd\_i2c.print("Display   ");
     \*\*Display = iCount++;         // set test value - works 
     lcd\_i2c.print(\*\*Display);   // display is OK 
     //         lcd\_i2c.setCursor(0, 3);
     //         lcd\_i2c.print("mask center ");
     //         lcd\_i2c.print(\*\*image );
     \*\*Display++;
     delay(500);

David Crow

Vaclav_Sal wrote:

Display = new int *[10]; // display rows
for (int i = 0; i < 20; i++)

I question this. Shouldn't the for() loop only run 10 times instead of 20?

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Lost User

You have two main problems. Firstly you create 10 rows and then try to initialise 20 of them each with 10 columns, try:

int **Display = new int *[10]; // display rows
for (i = 0; i < 10; i++) // initialise each of 10 rows
Display[i] = new int[20]; // with 20 columns

When adding your counter values into the array you increment your Display pointer (which indexes the rows only), which means that after 10 iterations it is pointing to an invalid address. Try using the offset values for row and column instead, as it will also make your code clearer, thus:

// iterate through the 10 rows
for ( i = 0; i < iRow; i++)
{
// for each column in the current row
for (j = 0; j < iCol; j++)
{
// set the value of count
Display[i][j] = iCount;
++iCount;
}
}

Vaclav_

Thanks, I was pretty sure I was doing it wrong using pointers while assigning the values. I also had the pointers array redefined in constructor. Sure would be easier with real debugger, oh well. Now it plays nicely. Thanks Cheers Vaclav

Lost User

Happy to help.

Vaclav_Sal wrote:

I was pretty sure I was doing it wrong using pointers

I had to think for quite a while about that before I realised why it was not working.

4india

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Albert Holguin

You responded to me, not OP.