Go的cgo C struct字段访问：下划线还是下划线？

Question

I'm running into a disconnect between the online documentation and the behavior I see in my programs accessing C structs within GO code. go version says I am using:

go version go1.4.2 linux/amd64

According to the GO CGO documentation:

Within the Go file, C's struct field names that are keywords in Go can be accessed by prefixing them with an underscore: if x points at a C struct with a field named "type", x._type accesses the field. C struct fields that cannot be expressed in Go, such as bit fields or misaligned data, are omitted in the Go struct, replaced by appropriate padding to reach the next field or the end of the struct.

I had troubles with this, so made a quick sample program to test it out:

package main
// struct rec
// {
//      int    i;
//      double d;
//      char*  s;
// };
import "C"
import "fmt"
func main() {
        s := "hello world"
        r := C.struct_rec{}
        r.i = 9
        r.d = 9.876
        r.s = C.CString(s)
        fmt.Printf("
\tr.i: %d
\tr.d: %f
\tr.s: %s
", 
                r.i, 
                r.d, 
                C.GoString(r.s))
}

When I use underscores as the docs indicate (eg, substitute r._i for r.i above) I get the following compile error:

r._i undefined (type C.struct_rec has no field or method _i)

When I don't use underscores it works fine. I tried this with both pointers and non-pointers. The only other idea I can think of is that maybe it's because I allocated the instances in GO rather than C, is that the case??

Thanks for any help!

Answer 1

The answer is in the very quote you have in your question:

Within the Go file, C's struct field names that are keywords in Go can be accessed by prefixing them with an underscore(…)

i, d, and s are not keywords in Go.