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/e0b9351e-83ea-4d9f-9b1c-756385c9a132n%40googlegroups.com.
