go: cmd/cgo: C.malloc does not support comma error return values

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?

$ go version
go version go1.6.2 windows/amd64

1. What operating system and processor architecture are you using (go env)?

$ go env
set GOARCH=amd64
set GOBIN=
set GOEXE=.exe
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=C:\Users\Administrator\Go
set GORACE=
set GOROOT=C:\go
set GOTOOLDIR=C:\go\pkg\tool\windows_amd64
set GO15VENDOREXPERIMENT=1
set CC=gcc
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0
set CXX=g++
set CGO_ENABLED=1

1. What did you do?

I ran cgom.go whose source is at https://play.golang.org/p/lFkVjkjn5W

1. What did you expect to see?

In cgo manual (https://golang.org/cmd/cgo/), the manual states that

Any C function (even void functions) may be called in a multiple assignment context to retrieve both the return value (if any) and the C errno variable as an error (use _ to skip the result value if the function returns void). For example:

I think C.malloc is C function. And Any C function may be called in a multiple assignemt context. Therefore, C.malloc should be called in a multiple assignment.

The idea was correct only if compilation would be successful.

1. What did you see instead?

$ go run cgom.go
# command-line-arguments
.\cgom.go:22:12: no two-result form for C.malloc

Unfortunately, reality is not. C.malloc cannot be used in that way, even though free function can be used in that way.

C.malloc function seems not to be part of a set of C functions, because contraposition of “Any C function may be called in a multiple assignment context” is “if a function may not be called in a multiple context, then the function is not C function”.

This contradicts usual idea that malloc should be C function. Go override some of special functions as malloc, etc. But these functions do not act like C functions.