Another update from ingydotnet^djgoku

Task/Use-another-language-to-call-a-function/Go/use-another-language-to-call-a-function-3.go

@@ -0,0 +1,45 @@
+// This buildmode requires the package to be main
+package main
+
+// Import C so we can export the function to C and use C types
+
+//#include <stdlib.h> // for size_t
+import "C"
+
+// Import reflect and unsafe so we can wrap the C array in a Go slice
+import "reflect"
+import "unsafe"
+
+// This buildmode also requires a main function, but it is never actually called
+func main() {}
+
+// The message to copy into the buffer
+const msg = "Here am I"
+
+// Here we declare the Query function using C types and export it to C
+
+//export Query
+func Query(buffer *C.char, length *C.size_t) C.int {
+        // Check there is enough space in the buffer
+        if int(*length) < len(msg) {
+                return 0
+        }
+
+        // Wrap the buffer in a slice to make it easier to copy into
+        sliceHeader := reflect.SliceHeader {
+                Data: uintptr(unsafe.Pointer(buffer)),
+                Len: len(msg),
+                Cap: len(msg),
+        }
+        bufferSlice := *(*[]byte)(unsafe.Pointer(&sliceHeader))
+
+        // Iterate through the message and copy it to the buffer, byte by byte
+        for i:=0;i<len(msg);i++ {
+                bufferSlice[i] = msg[i]
+        }
+
+        // Set length to the amount of bytes we copied
+        (*length) = C.size_t(len(msg))
+
+        return 1
+}