Okay, will store the pointer directly in a struct as a private field. Thanks for your time and input, I greatly appreciate it.
Tamás Gulácsi schrieb am Freitag, 9. Juli 2021 um 14:17:48 UTC+2: > The runtime and checks does not know what's inside an uintptr, so > converting an uintptr to a(n unsafe.)Pointer > triggers the warnings. Only the special specified cases are legal. > > TL;DR; Do not use uintptr. > (More elaborate: do not use an uintptr to store and retrieve a pointer - > just store the pointer directly). > > Tamas > > snmed a következőt írta (2021. július 9., péntek, 11:26:48 UTC+2): > >> Yes uintptr is the address the C pointer is pointing to , right? So C >> doesn't move any memory and therefore the address is still valid until >> deleted in C code. >> If I take the value of uintptr variable, convert it back with >> unsafe.Pointer(uintptr) and pass it to a C function, does C not interpret >> that as a C pointer pointing to the same address as uintptr holds? >> Therefore the conversion should be alright? >> >> Sorry for not getting it... >> >> Sandro >> >> Tamás Gulácsi schrieb am Freitag, 9. Juli 2021 um 11:12:22 UTC+2: >> >>> An uintptr *is not a pointer*, so 2. is false. >>> NOTHING at Go's side holds anything regarding MyAppHwnd, and it doesn't >>> seem to be a pointer at all (just a number), >>> so converting that to an unsafe.Pointer is unsafe. >>> >>> The rules about uintptr are there for a reason! >>> Only the allowed use cases are guaranteed to have the desired effect, by >>> preventing any memory movement >>> int that block of code. >>> >>> Tamas >>> snmed a következőt írta (2021. július 9., péntek, 8:21:37 UTC+2): >>> >>>> Thx Ian to pointing me to the documentation I read it, but still unsure >>>> regarding my example. Probably rule number 4 could apply, so let me go >>>> through my example and correct me if I'm wrong. >>>> >>>> 1. C.CreateApp() creates memory in C code and returns it as C void >>>> pointer >>>> 2. Go function CreateApp() returns that as MyAppHwnd (uintptr ) so >>>> MyAppHwnd contains a valid C memory address >>>> 3. app variable holds still a valid C memory address as long as it is >>>> not deleted in C code >>>> 4. So calling ShowApp() it should be legit to convert MyAppHwnd back >>>> to an unsafe.Pointer and cast it to C.MyAppPtr. It is still a valid memory >>>> address in C and therefore should be interpreted as pointer in C, right? >>>> >>>> So therefore the warning can be ignored or do I miss something >>>> important? >>>> >>>> Cheers >>>> Sandro >>>> >>>> >>>> Ian Lance Taylor schrieb am Freitag, 9. Juli 2021 um 05:37:16 UTC+2: >>>> >>>>> On Thu, Jul 8, 2021 at 10:09 AM snmed <sandro....@gmail.com> wrote: >>>>> > >>>>> > Thanks for your reply. I came across a similar solution today, I >>>>> made a struct which is visible outside the package and use a private >>>>> field >>>>> myApp C.MyAppPtr to hide the C type. >>>>> > I still wondering why the uintptr version works but shows a warning >>>>> "possible misuse of unsafe.pointer", CGO documentation is not very clear >>>>> to >>>>> me about the intricacies of type conversions between Go and C. >>>>> >>>>> There is a very limited number of cases in which it is OK to convert a >>>>> pointer to uintptr. Those cases are described at >>>>> https://golang.org/pkg/unsafe. >>>>> >>>>> Ian >>>>> >>>> -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/b63866bd-d536-477c-bc7b-43cf791f4490n%40googlegroups.com.
