How do I set errno from Go

Question

I have a C function calling a Go routine via cgo. I need to Go routine to set the errno correctly so the C thread can inspect it's errno and act accordingly. Unable to google on how to set the errno via Go

Answer 1

Just to clarify, you can still set it via C-function that you call via cgo.

package main

// #include <errno.h>
// #include <stdio.h>
//
// void setErrno(int err) {
//      errno = err;
// }
//
import "C"

func main() {
        C.setErrno(C.EACCES)
        C.perror(C.CString("error detected"))
        C.setErrno(C.EDOM)
        C.perror(C.CString("error detected"))
        C.setErrno(C.ERANGE)
        C.perror(C.CString("error detected"))
}

On my system it outputs

error detected: Permission denied
error detected: Numerical argument out of domain
error detected: Numerical result out of range