Function causes a crash

[Hector1945]

Hello !
So recently I have been working on a recreation of Tennis For Two:

And I used this function to display the trail of the ball:

and traillength = 50

But as soon as I added it to the code, Fuze started crashing. Approximately 20 seconds in the game, Fuze closes and I get the "The software was closed because an error occured" error. This is probably a bug, since Fuze crashing is never a feature. But I have absolutely no idea what causes the bug. It is probably a bit of an error of mine, too. What could I do to get rid of it ?
Thanks.

[DaddyJDM]

Since that is called in a loop, creating a shape each iteration will eat memory. You can try deleting the shape after it is drawn to clean up.
Alternatively, you can just draw the line, I think with the ' line ' function?

[Hector1945]

@DaddyJDM Well actually, I tested it with the "drawing" part commented, like in the picture, and it didn't change anything...

[Jongjungbu]

What about that CreateLine() also

[Gothon]

The negative step loop might be the culprit here. Fuze doesn't do these loops the way you would expect it to.
Replace:
for i = len(trail)-1 to -1 step -1 loop
with
for i = len(trail)-1 to 0 loop
and see if that works. I suspect Fuze may have been crashing on reading trail[-1] because the loop doesn't stop at 0 like the positive step loops do. Also the sign of the step is unneeded because Fuze determines the direction from the start and stop values.

[DaddyJDM]

It can be worth trying to replace
Trail[0]=[{ball.x,ball.y},moving]
With
Trail[0][0]={ball.x,ball.y}
Trail[0][1]=moving

That might avoid unnecessary creation of arrays through each loop?

[Hector1945]

@Jongjungbu Fuze still crashes when I don't use it, so pretty sure it only comes from the first part of the function.

[Hector1945]

@Gothon There is no crash anymore, but if I uncomment the second part of the function, the trail doesn't display anymore, while it used to...

[Hector1945]

@DaddyJDM I get an error for attempting to index non array type

[spikey]

@Hector1945 wow, the response time is quite fast here 😄 @Gothon +1, @DaddyJDM +1 even go with:

trail[0]=[] //the first time
trail[0][0]={} //the first time
trail[0][0].x=ball.x
trail[0][0].y=ball.y

[Hector1945]

@spikey Why do I get a "unrecognized type: 4" on the line 79 ?

[Gothon]

There is actually another caveat. If len(trail) is 1, the loop will become for i = 0 to 0 flipping to positive direction and not iterate. There are a couple ways of avoiding this problem. You can write a while loop or use

for j = 0 to len(trail) loop
    i = len(trail) - 1 - j

Though I notice that your loop uses both trail[i] and trail[i+1], so you probably need to write it as:

for j = 0 to len(trail)-1 loop
    i = len(trail) - 2 - j
    ...
repeat

so that it loops len(trail)-2 through 0 since anything outside that range will give you an out of bounds array index.

[Hector1945]

So I tried replacing

for i = len(trail)-1 to -1 step -1 loop

with

for i = len(trail)-1 to 0 loop

and starting the game with 2 values already in the array, and the trail works, but I still get the crash...

[Gothon]

@Hector1945 said in Function causes a crash:

but I still get the crash...

Right the first value of i is len(trail)-1 = 1 and i+1 = 2 which is out of bounds for an array of size 2 (the valid indices are 0, 1). Since you are writing trail[i+1], you need to start the loop with for i = len(trail)-2 ....

[PickleCatStars]

I had ’unrecognised type’ error before when accessing an array. Martin said to change the iterator Name to something unique (the ’x’ in ’for x = 0 to..’), and that worked. It was a fuze bug, not something I’d done that time...

[Hector1945]

@Gothon Wouldn't I get an error if it was out of bounds ? Because the crash only occurs like 20 seconds in the game, way after the array gets completely filled with 50 values...

[Gothon]

@Hector1945 I agree that Fuze should give you an out of bounds error, but when Fuze itself is crashing it is difficult to know what to expect. It can be tricky to trace back to the cause of undefined behaviors.

[Hector1945]

If I do the len(trail)-2 it does not crash but the trail doesn't display properly

[Hector1945]

Oh ok it just didn't execute the command because len(trail)-2 = 0 if trail has 2 values

[spikey]

@Hector1945 Glad you solved it , the unrecognized type 4 error probably went from adding a value to a not properly initialized array (or reading from a such). (Because of wrong dimension, index). Is it technically a 'void' type? What means its just pointing to a place in memory, but its not clear yet, what the bytes mean there: number, string, array. If somebody knows for sure please comment on this. It would be nice to know for sure.