Can you change a variables pointer?
BlitzMax Forums/BlitzMax Programming/Can you change a variables pointer?
| ||
| Can Blitzmax modify an existing variables pointer? i.e. local a = 10 local b = 25 Can we change 'a' pointer so it is looking at 'b'? This is very important for returned pointers from a Dll to an existing type structure in memory. Getting pointers with varptr is easy , changing them is not! |
| ||
| Yeah. You'd need to use some pointer variables alongside them though. Or put them in a type. local a=10 local b=25 would need.. local c:Int Ptr=varptr(a) local d:Int Ptr=varptr(b) Then think of your variable with c[0] and d[0] instead of a and b ie c=d ' make a look at b print c[0] ' same as print a print d[0] ' same as print b c[0]=5 ' same as a=5 d[0]=15 ' same as b=15 |
| ||
| Function pointers can do more of what you're thinking of , more directly changing to point to another function. I don't think you can change variable pointers, they are internal, without using a explicit pointer variable to manage it manually. I expect Max uses a pointer behind the scenes which is not accessible to your app. |
| ||
| Thank you for your info. I will have to find anothewr way! |
| ||
| Can we change 'a' pointer so it is looking at 'b'? No. This is very important for returned pointers from a Dll to an existing type structure in memory. But you can do that. |
| ||
| Have you looked at CreateStaticbank() ? You can point that at an existing memoryblock. |
| ||
| You can cludge a static bank onto a variable Local a:Int=5 Local bnk:TBank=CreateStaticBank(VarPtr(a),4) Local buf:Int Ptr=Int Ptr(BankBuf(bnk)) buf[0]=10 'same as a=10 print buf[0] 'same as print a |
| ||
| Ziltch: local a = 10 You could write:local b = 25 local a[] = [10] If you now want to change a so that it's looking at b you can write:local b[] = [25] a = b To access to the values of the variables use a[0] instead of a and b[0] instead of b.This allows you two ways of setting the variable to a value: a[0]=8 'This sets a and all variables looking at a to 8. a=[8] 'This sets only a to 8; other variables looking at a will stay at their old values. Ziltch: Getting pointers with varptr is easy , changing them is not! A pointer to a variable is a constant - so you can't change it. |
| ||
| Thanks for the handy info. The CreateStaticBank command may help. Thanks Peter and AngelDaniel. Fabian , I also did not know you could do , a=[8] . Thanks! |
   |