const pointers

[codifiesParticipant]

in a module I have something like this

Monkey

Struct constFloat="const float" Function someFunction:constFloat ptr()

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Struct constFloat="const float"   Function someFunction:constFloat ptr()

which I use like this

Monkey

Local mypointer:Float Ptr = Cast<Float Ptr>(someFunction()) print mypointer[4] ' its a const pointer to an array of floats

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Local mypointer:Float Ptr = Cast<Float Ptr>(someFunction())   print mypointer[4] ' its a const pointer to an array of floats

I gotta be doing this wrong ! it seems a bit fugly!!!

If I try to use a const pointer like a normal pointer I see g++ errors (off the top of my head about casting pointers)

[abakoboParticipant]

Defining extern with ‘const something’ is very limited. It can lead to some mess if you don’t use for functions arguments only. Because the transpiler will just copy the defined name and ‘const something’ is more than just the name on The C side. Mark has manualy made some glue code for these situation. For example for the chipmunk debugdraw drawpoly callback function that have a ‘const ptr’ as argument.
I had also a similar problem with pure virtual methods for the box2d wrap but I chose to remove the const in the cpp code because box2d is solid enough not to need the const barrier imo. So if you may remove ‘const’ from the C code, it’s probably the fastest way.
It’s one of the difficulties with c to mx2. The only one I encoutered for now.

[codifiesParticipant]

I *really* don’t want to modify the C++ code its a large code base and will require periodic updating

I am aware of what a const pointer is on the C side of things having used them in previous C projects, just a shame that MX2 doesn’t have some mechanism to handle them (or rather more gracefully) I might have misunderstood your reply but did you get that I am only using constFloat specifically where I need to handle a const pointer and no where else?

glue code could slow things down, an extra call per call when there could be the need to retrieve several hundred const pointers per drawn frame doesn’t seem ideal either…

Do you see any issues with my solution (given that yes it is a tad ungraceful) ?

[codifiesParticipant]

@abakobo

lol – now this server isn’t taking 30 seconds to serve a page, I managed to use the search…

seems I’m not the only one to “discover” the

Struct constFloat = “const float”

hack!

[abakoboParticipant]

Here some working code (with an int). But you probably already get it.. or may be this is not relevant at all but I wanted to play with the ‘cast’ solution for const ptr. And this is nothing official, so could be deprecated? Never saw it in the docs..

.monkey2

Monkey

[crayon-5cba90a195c38095812623 inline="true" ]#Import "<std>" #Import "facto_c.h" Extern Struct c_int="const int" End Function Factorial:c_int Ptr (M:int) Public Function Main() Local ci:c_int ptr Local ip:Int Ptr ci=Factorial(4) 'should be 24.. ip = Cast<int Ptr>(ci) Print ip[0] End

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[crayon-5cba90a195c38095812623 inline="true" ]#Import "<std>" #Import "facto_c.h" Extern   Struct c_int="const int" End Function Factorial:c_int Ptr (M:int) Public   Function Main() Local ci:c_int ptr Local ip:Int Ptr ci=Factorial(4) 'should be 24.. ip = Cast<int Ptr>(ci) Print ip[0] End

[/crayon]

facto_c.h:

Monkey

[crayon-5cba90a195c42942053325 inline="true" ]const int* Factorial(int M) { int factorial=1; int* returner; for(int i=1; i<=M; i++) { factorial = factorial*i; } returner=&factorial; return returner; //' returning directly &factorial was not working, it had to be assigned to a 'named' int pointer }

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[crayon-5cba90a195c42942053325 inline="true" ]const int* Factorial(int M) {    int factorial=1;    int* returner;      for(int i=1; i<=M; i++)    {       factorial = factorial*i;    }    returner=&factorial;    return returner; //' returning directly &factorial was not working, it had to be assigned to a 'named' int pointer }

[/crayon]

[codifiesParticipant]

yeah – thanks, that is basically what I’m doing and checking the generated code afaict its doing what I’d have done using C

I assume you realise you don’t need the ci pointer, ie

Monkey

Local ip:Int Ptr ip = Cast<int Ptr>(Factorial(4)) Print ip[0]

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Local ip:Int Ptr   ip = Cast<int Ptr>(Factorial(4)) Print ip[0]

looking at a different example

Monkey

Local pos:float ptr = Cast<float ptr>(dGeomGetPosition(geom)) '// redraw sphere at new location

1	Local pos:float ptr = Cast<float ptr>(dGeomGetPosition(geom)) '// redraw sphere at new location

gets you

Monkey

bbFloat* l_pos=((bbFloat*)(dGeomGetPosition(g_default_geom)));

1	bbFloat* l_pos=((bbFloat*)(dGeomGetPosition(g_default_geom)));

Which looks sane to me!

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