如何从C函数获取out参数？

I have a C function as below:

void sign(const char *in, int in_size, char *out, int *out_size);

How do I use it in Go?

Am I correct?

data:="123456"
cData := C.CString(data)
defer C.free(unsafe.Pointer(cData))

var _skcy [30]C.char
var outLen C.int
C.sign(cData, C.int(len(data)), &_skcy[0], &outLen)

skcy := C.GoStringN(&_skcy[0], outLen-1)