unexpected type: ... with cgo in Go

Question

I'm new to Go and trying to learn how to call C from Go. I wrote this program to open a named semaphore, get the value and print it to the screen. When I run it go build semvalue.go I get the error: ./semvalue.go:16:14: unexpected type: ...

What does this mean? What am I doing wrong?

package main import "fmt" // #cgo LDFLAGS: -pthread // #include <stdlib.h> // #include <fcntl.h> // #include <sys/stat.h> // #include <semaphore.h> import "C" func main() { name := C.CString("/fram") defer C.free(name) fram_sem := C.sem_open(name, C.O_CREAT, C.mode_t(0644), C.uint(1)) var val int ret := C.sem_getvalue(fram_sem, val) fmt.Println(val) C.sem_close(fram_sem) }

Thank you.

Mr_Pink · Accepted Answer · 2014-11-10 21:20:36Z

The message is confusing, until you realize that the ... is the variadic portion of a C function. You can't use C variadic functions directly from Go, so you'll have to write a small wrapper in C to call sem_open.

A couple more notes:

C.free should be called with C.free(unsafe.Pointer(name))
val needs to be a *C.int
sem_getvalue uses errno, so you should call it with ret, err := C.sem_getvalue...

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