From 505fa7b42338f0aba7e4235acbc8274a20f3c1f0 Mon Sep 17 00:00:00 2001 From: Ian Lance Taylor Date: Tue, 12 Jan 2016 07:03:28 -0800 Subject: [PATCH] cmd/cgo: document C.sizeof_T and zero-sized field restriction Update #9401. Update #11925. Update #13919. Change-Id: I52c679353693e8165b2972d4d3974ee8bb1207ef Reviewed-on: https://go-review.googlesource.com/18542 Run-TryBot: Ian Lance Taylor TryBot-Result: Gobot Gobot Reviewed-by: Russ Cox --- src/cmd/cgo/doc.go | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/src/cmd/cgo/doc.go b/src/cmd/cgo/doc.go index 8ec4301112..bd38a5c153 100644 --- a/src/cmd/cgo/doc.go +++ b/src/cmd/cgo/doc.go @@ -125,11 +125,19 @@ The C types __int128_t and __uint128_t are represented by [16]byte. To access a struct, union, or enum type directly, prefix it with struct_, union_, or enum_, as in C.struct_stat. +The size of any C type T is available as C.sizeof_T, as in +C.sizeof_struct_stat. + As Go doesn't have support for C's union type in the general case, C's union types are represented as a Go byte array with the same length. Go structs cannot embed fields with C types. +Go code can not refer to zero-sized fields that occur at the end of +non-empty C structs. To get the address of such a field (which is the +only operation you can do with a zero-sized field) you must take the +address of the struct and add the size of the struct. + Cgo translates C types into equivalent unexported Go types. Because the translations are unexported, a Go package should not expose C types in its exported API: a C type used in one Go package