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/e6e655f5-bf38-4d82-80d8-259a054e9138n%40googlegroups.com.
