cgo: C.uchar array or pointer cannot be assigned to uint8 array or pointer

[bits01]

package main

import "C"

import "fmt"

func main() {
    var cp *C.uchar
    var gop *uint8 = cp
    fmt.Println(gop)

    var carr [1]C.uchar
    var goarr [1]uint8 = carr
    fmt.Println(goarr)
}

Trying to run it:

./main.go:9: cannot use cp (type *C.unsignedchar) as type *uint8 in assignment
./main.go:13: cannot use carr (type [1]C.unsignedchar) as type [1]uint8 in assignment

If I run go tool cgo -godefs it generates a Go file that looks and runs fine:

...
func main() {
        var cp *uint8
        var gop *uint8 = cp
        fmt.Println(gop)

        var carr [1]uint8
        var goarr [1]uint8 = carr
        fmt.Println(goarr)
}

Not sure whether this is the same issue as #13635 that I also reported a few days ago and has been fixed.

Is it possible to land a fix for the above in 1.5.x please?

[minux]

This is working as intended. uint8 and C.uchar are not the same type, according to the Go rules. You can think of C.uchar as type C.uchar uint8 Because it's a named type whose underlying type is uint8, the type is different from uint8. As an example, even this won't compile for the same reason: var c1 C.uchar var c2 uint8 = c1

[bits01]

I see. I was under the impression that C.uchar works more like the pre-declared byte alias for uint8. Thank you. What confused me was the generated go file when using cgo -godefs

[minux]

cgo -godefs output is not the file generated for cgo, it's used to generate various structs/consts that are equivalent to existing C interface for the syscall and runtime package. The cmd/cgo help message made that clear: -godefs for bootstrap: write Go definitions for C file to standard output It's only intended to use when bootstrapping Go on a new platform.

[bits01]

Thanks for clarifying. I think somewhere in the group or in some post someone recommended to look at the output of cgo -godefs. Lots of conflicting and sometimes misleading info out there.

[bits01]

I may have taken what you posted here out of context, sorry.
http://grokbase.com/t/gg/golang-nuts/12cemmrhk5/go-nuts-cgo-cast-c-struct-to-go-struct