update book code

eBook/examples/chapter_12/json.go

@@ -0,0 +1,40 @@
+// json.go.go
+package main
+
+import (
+	"fmt"
+	"encoding/json"
+	"log"
+	"os"
+)
+
+type Address struct {
+	Type             string
+	City             string
+	Country          string
+}
+
+type VCard struct {
+	FirstName	string
+	LastName	string
+	Addresses	[]*Address
+	Remark		string
+}
+
+func main() {
+	pa := &Address{"private", "Aartselaar","Belgium"}
+	wa := &Address{"work", "Boom", "Belgium"}
+	vc := VCard{"Jan", "Kersschot", []*Address{pa,wa}, "none"}
+	// fmt.Printf("%v: \n", vc) // {Jan Kersschot [0x126d2b80 0x126d2be0] none}: 
+	// JSON format:
+	js, _ := json.Marshal(vc)
+	fmt.Printf("JSON format: %s", js)
+	// using an encoder:
+	file, _ := os.OpenFile("vcard.json", os.O_CREATE|os.O_WRONLY, 0)
+	defer file.Close()
+	enc := json.NewEncoder(file)
+	err := enc.Encode(vc)
+	if err != nil {
+		log.Println("Error in encoding json")
+	}
+}