Bug in Pointer Arrays?

[Mike Thomson]

Hi All,

Is this a bug?

I have an application for a motel reservation system. I am trying to build a matrix array of Units/Dates to be used for the purpose of a dyanmic list box showing what units have been booked. My problem is that after I have filled the Array the first element has the same value throughout. If you run the following code you will see what I mean

****** START *****

trace.clear()
sUnits = "Unit1,Unit2,Unit3,Unit4,Unit5,Unit6,Unit7,Unit8,Unit9,Unit10"
sUnits=stritran(sUnits,",",crlf())
dim aUnits[10] as C
dim aMatrix[10,31] as P
aUnits.initialize(sUnits)

dDate = {01-07-2005}
for i = 1 to 10
for j = 1 to 31
aMatrix[i,j].Date = dDate + j -1
aMatrix[i,j].Unit = aUnits[i]
next j
next i

for j = 1 to 30
trace.writeln (cdate(aMatrix[1,j].date)+ "/" + aMatrix[1,j].Unit + " " + \
cdate(aMatrix[2,j].date) + "/" + aMatrix[2,j].Unit)

next j

***** END *****

The results displayed in the trace window are as follows (first 8 days only)

20050731/Unit1 20050701/Unit2
20050731/Unit1 20050702/Unit2
20050731/Unit1 20050703/Unit2
20050731/Unit1 20050704/Unit2
20050731/Unit1 20050705/Unit2
20050731/Unit1 20050706/Unit2
20050731/Unit1 20050707/Unit2
20050731/Unit1 20050708/Unit2

Notice how for Unit 1 the Dates are all the same

Any Suggestions?

[Tom Cone Jr]

RE: Bug in Pointer Arrays?

Assuming {01-07-2005} is July 1,2005 on your side of the pond I get the same results here.

-- tom

[Tom Cone Jr]

RE: Bug in Pointer Arrays?

Mike,

I noticed that if I put a trace.writeln() statement inside the loop that populates the matrix the Unit1 date values appear correctly. ???

-- tom

[G Gabriel]

RE: Bug in Pointer Arrays?

Mike:
It's a bit subtle but easy to explain. It has nothing do do with your arry which is fine, but with the trace.writeln routine:
The trace.writeln writes the first row from the arry, then increments j by one but does not increment i, and as such, you keep reading the same value on the first row in the left column, while in the second column and as j increments, you keep reading down the column.

In summary, your array is compilled properly, but you are not reading it proprly.
Gabe

[Tom Cone Jr]

RE: Bug in Pointer Arrays?

gabe, this is admittedly slippery stuff for me, but I disagree with your analysis. Consider this example that illustrates the same issue:

'Date Created: 23-Jul-2005 08:35:58 AM
'Last Updated: 23-Jul-2005 08:35:58 AM
'Created By : TEC
'Updated By : TEC

trace.clear()
dDate = {01/01/2005}

'-----------loop 1 (using date type vars) works fine -------------
dim dArray[31] as D
for i = 1 to 31
dArray[i] = dDate + (i - 1)
next i
trace.writeln("Loop 1 begins")
for i = 1 to 31
trace.writeln(dtoc(dArray[i]))
next i
trace.writeln("Loop 1 ends")
'----------- loop1 ends here -----------------------------


'------------ loop 2 (using date type vars in a matrix array) works fine ------------
dim aMatrix[1,31] as D
for i = 1 to 31
aMatrix[1,i] = dDate + (i -1)
next i
trace.writeln("Loop 2 begins")
for i = 1 to 31
trace.writeln(dtoc(aMatrix[1,i]))
next i
trace.writeln("Loop 2 ends")
'------------ loop 2 ends ----------------------------------------------------------


'------------ loop 3 begins here (uses pointer data type) -------------------------
'In this loop the trace.writeln() statements immediately following the
' assignment statement are correctly processed.
'HOWEVER, when the matrix is processed a second time, for the next
' trace.writeln() statements, the wrong values appear.
dim pMatrix[1,31] as P
trace.writeln("Loop 3 begins")
for i = 1 to 31
pMatrix[1,i].MyDate = dDate + (i - 1)
trace.writeln(dtoc(pMatrix[1,i].MyDate) + " written as each pointer element is loaded")
next i
trace.writeln("-----------------------")
for i = 1 to 31
trace.writeln(dtoc(pMatrix[1,i].MyDate) + " written after all pointer elements were loaded")
next i
trace.writeln("Loop 3 ends")
'-------------- loop 3 ends here -----------------------------
trace.writeln("-----------------------")
trace.writeln(dtoc(pMatrix[1,1].MyDate)) 'returns correct value, but
trace.writeln(dtoc(pMatrix[1,7].MyDate)) 'returns wrong value
trace.writeln(dtoc(pMatrix[1,14].MyDate)) 'returns wrong value
trace.writeln(dtoc(pMatrix[1,21].MyDate)) 'returns wrong value
end

[G Gabriel]

RE: Bug in Pointer Arrays?

Tom:
My head is spinning from all these loops! Here is the routine after I modified it and the result:

trace.clear()
for j = 1 to 5
sUnits = "Unit1,Unit2,Unit3,Unit4,Unit5,Unit6,Unit7,Unit8,Unit9,Unit10"
sUnits=stritran(sUnits,",",crlf())
dim aUnits[10] as C
dim aMatrix[10,31] as P
aUnits.initialize(sUnits)

dDate = {07-01-2005}
for i = 1 to 10
aMatrix[i,j].Date = dDate + j -1
aMatrix[i,j].Unit = aUnits[i]
next i

trace.writeln (cdate(aMatrix[1,j].date)+ "/" + aMatrix[1,j].Unit + " " + \
cdate(aMatrix[2,j].date) + "/" + aMatrix[2,j].Unit)
next j

20050701/Unit1 20050701/Unit2
20050702/Unit1 20050702/Unit2
20050703/Unit1 20050703/Unit2
20050704/Unit1 20050704/Unit2
20050705/Unit1 20050705/Unit2

Gabe

[Tom Cone Jr]

RE: Bug in Pointer Arrays?

Gabe,

I'm getting a bit dizzy, also. "grin"

Your script stops short of the problem area. The array elements appear to be populated correctly, but if you then extend the script to re-display the exact same elements you will encounter the problem under discussion.

e.g.

'Date Created: 23-Jul-2005 02:17:57 PM
'Last Updated: 23-Jul-2005 02:17:57 PM
'Created By : gabe
'Updated By : tom
trace.clear()
for j = 1 to 5
sUnits = "Unit1,Unit2,Unit3,Unit4,Unit5,Unit6,Unit7,Unit8,Unit9,Unit10"
sUnits=stritran(sUnits,",",crlf())
dim aUnits[10] as C
dim aMatrix[10,31] as P
aUnits.initialize(sUnits)

dDate = {07-01-2005}
for i = 1 to 10
aMatrix[i,j].Date = dDate + j -1
aMatrix[i,j].Unit = aUnits[i]
next i

trace.writeln (cdate(aMatrix[1,j].date)+ "/" + aMatrix[1,j].Unit + " " + \
cdate(aMatrix[2,j].date) + "/" + aMatrix[2,j].Unit)
next j

'Now that the array is populated, attempt to display the same elements
'as were just written to the trace window (using the same code to do so)
trace.writeln("-------------------")
for j = 1 to 5
trace.writeln (cdate(aMatrix[1,j].date)+ "/" + aMatrix[1,j].Unit + " " + \
cdate(aMatrix[2,j].date) + "/" + aMatrix[2,j].Unit)
next j

[Mike Thomson]

RE: Bug in Pointer Arrays?

I tried reading the Array outside the trace.writeln script and I get still get the wrong values.

So I guess at this stage we probably agree thats theres a problem

How do these things normally get reported to Alpha Software for review?

[Tom Cone Jr]

RE: Bug in Pointer Arrays?

The Help menu w/in Alpha Five itself has a "Send bug report" option. I submitted a report this afternoon.

-- tom

[Mike Thomson]

RE: Bug in Pointer Arrays?

Great,

While I am an experienced Database developer - I am still only evaluating Alpha 5 for my next commercial project. In doing so I am tending to start at the more complex things and work backwards.

Despite its present client server limitations I am veryimpressed.

It is refreshing to see how well this forum is supported.

Many Thanks
Mike Thomson

[Tom Cone Jr]

RE: Bug in Pointer Arrays?

Mike,

You're welcome.

To round out your "sampling" experience, be sure to visit and browse:

1) Newsletter archives online
2) Code Archive forum in this message board
3) Articles collection at www.learn alpha.com
4) The tutorials and other resources at Alpha's online Learning Center (link found on Alpha Software's home page)

-- tom

[G Gabriel]

RE: Bug in Pointer Arrays?

Mike:
have youtried the script as I modified it? it seems to bring the desired results.
Gabe

[AaronBBrown]

RE: Bug in Pointer Arrays?

We discovered a problem with multidimensional arrays where the [1,x] entry doesn't work as expected (as evidenced by your example), but anything [2,x] or greater does. Here is a simple example that shows the issue:

delete p
dim p[5,5] as p
p[1,1].name = "aaron"
p[1,2].name = "selwyn"
p[2,1].name = "cian"
p[2,2].name = "eavan"
p[3,1].name = "brett"
p[3,2].name = "adi"

? p[1,1].name
= "selwyn"

? p[1,2].name
= "selwyn"

? p[2,1].name
= "cian"

? p[2,2].name
= "eavan"

? p[3,1].name
= "brett"

? p[3,2].name
= "adi"


I will add this to the list of bugs to be fixed, but in the meantime, could you please elaborate on what you are trying to accomplish and perhaps we can come up with a better solution or a workaround.

One option would to be to use a property array with a month value and date value, or a faked multidimensional array ala

dim row[12] as p
dim row[1..12].col[31] as d

row[3].col[21] = date()

etc

[Mike Thomson]

RE: Bug in Pointer Arrays?

Thanks Aaron,

The reason I was using a multi dimendional arrays was to hold data for for a dyanmic grid which related to a grid of buttons , each button being colour coded to show the availability of the room. The reason I have used buttons is that they allow me to provide a graphical presentation.

Please note the thread - which has an example of grid , and I have reported problem relating to time it takes to update controls.
http://msgboard.alphasoftware.com/alphaphorum/read.php3?num=15&id=22035&loc=0&offset=0&sortby=lastreply&direction=desc&thread=22035

The X a-axis for the Grid is a range of dates (14 at a time) and a range of units (a total of 22). I was using the Array to hold varios data associated with each cell , such as date, status, customer etc.

At the end of the day I ended up doing the same as you have suggested and it worked OK. - But the speed of updating controls is still an issue.

Mike