cmd/cgo: Go type not supported in export: struct #18412
Comments
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You can only export basic function signatures. @ianlancetaylor, are the rules documented somewhere? |
bradfitz
changed the title
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The documentation, in https://golang.org/cmd/cgo, is "Not all Go types can be mapped to C types in a useful way." That said, struct types could be handled better than they are. Right now they are a TODO in cmd/cgo/Package.cgoType. Because of that TODO, you can't //export a Go function that uses a struct type. And, frankly, using it in C would be tricky, since C does not have But, of course, we should find a way to make this work. This issue can track that. |
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Actually, I think this is working as intended.
The correct program should use a type defined in C, rather than in Go,
because otherwise the external C programs have to manually define
a C struct matching the Go struct, which is non-trivial and error-prone.
(cgo is about interfacing C to Go, not about making Go interfaces
available to C, so it's understandable that cgo doesn't support exporting
arbitrary Go types to C -- you should do the other way around, and
define the necessary structs in C.)
For example, this works today:
package main
/*
struct Vertex {
int X;
int Y;
};
*/
import "C"
import "fmt"
//export getVertex
func getVertex(X, Y C.int) C.struct_Vertex {
return C.struct_Vertex{X, Y}
}
func main() {
fmt.Println(getVertex(1, 2))
}
[Edit: restored indentation in the code.]
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I'll keep this open as a documentation CL. |
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Change https://golang.org/cl/52852 mentions this issue: |
go version
go version go1.7.4 linux/amd64
go env
What did you do?
I am trying to build a shared object from go code (code has a struct and some functions). I am exporting all the functions and then run go build, but I see this error:
Go type not supported in export: struct. There's this thread on the go-nuts mailing list about this issue, but there doesn't seem to be a resolution.Here's an example program that generates the error:
vertex.go
go build commandline output
What did you expect to see?
I expect the
go buildto run successfully, and generate the shared object.What did you see instead?
I see an error
Go type not supported in export: struct.The text was updated successfully, but these errors were encountered: