Golang CGo: converting union field to Go type

Question

I\'m working with this C struct on a 64 bit platform, trying to access the ui32v field in the value union:

struct _GNetSnmp         


        

Answer 1

Sonia already answered her own question, I just want to provide the reason for why two type conversions are necessary.

From the documentation for unsafe.Pointer:

1) A pointer value of any type can be converted to a Pointer.

2) A Pointer can be converted to a pointer value of any type.

3) A uintptr can be converted to a Pointer.

4) A Pointer can be converted to a uintptr.

Since var ptr uint64 is not a pointer (as type uint64 is not a pointer), ptr cannot be converted directly to unsafe.Pointer using rule 1. Therefore it is necessary to first convert ptr to uintptr, then from uintptr to a Pointer following rule 3.