JSON unmarshal: all values are zero [duplicate] - json

Question

I need to decode a JSON string with the float number like:
{"name":"Galaxy Nexus", "price":"3460.00"}
I use the Golang code below:
package main
import (
"encoding/json"
"fmt"
)
type Product struct {
Name string
Price float64
}
func main() {
s := `{"name":"Galaxy Nexus", "price":"3460.00"}`
var pro Product
err := json.Unmarshal([]byte(s), &pro)
if err == nil {
fmt.Printf("%+v\n", pro)
} else {
fmt.Println(err)
fmt.Printf("%+v\n", pro)
}
}
When I run it, get the result:
json: cannot unmarshal string into Go value of type float64
{Name:Galaxy Nexus Price:0}
I want to know how to decode the JSON string with type convert.

Answer 1

The answer is considerably less complicated. Just add tell the JSON interpeter it's a string encoded float64 with ,string (note that I only changed the Price definition):
package main
import (
"encoding/json"
"fmt"
)
type Product struct {
Name string
Price float64 `json:",string"`
}
func main() {
s := `{"name":"Galaxy Nexus", "price":"3460.00"}`
var pro Product
err := json.Unmarshal([]byte(s), &pro)
if err == nil {
fmt.Printf("%+v\n", pro)
} else {
fmt.Println(err)
fmt.Printf("%+v\n", pro)
}
}

Answer 2

Just letting you know that you can do this without Unmarshal and use json.decode. Here is Go Playground
package main
import (
"encoding/json"
"fmt"
"strings"
)
type Product struct {
Name string `json:"name"`
Price float64 `json:"price,string"`
}
func main() {
s := `{"name":"Galaxy Nexus","price":"3460.00"}`
var pro Product
err := json.NewDecoder(strings.NewReader(s)).Decode(&pro)
if err != nil {
fmt.Println(err)
return
}
fmt.Println(pro)
}

Answer 3

Avoid converting a string to []byte: b := []byte(s). It allocates a new memory space and copy the whole the content into it.
strings.NewReader interface is better. Below is the code from godoc:
package main
import (
"encoding/json"
"fmt"
"io"
"log"
"strings"
)
func main() {
const jsonStream = `
{"Name": "Ed", "Text": "Knock knock."}
{"Name": "Sam", "Text": "Who's there?"}
{"Name": "Ed", "Text": "Go fmt."}
{"Name": "Sam", "Text": "Go fmt who?"}
{"Name": "Ed", "Text": "Go fmt yourself!"}
`
type Message struct {
Name, Text string
}
dec := json.NewDecoder(strings.NewReader(jsonStream))
for {
var m Message
if err := dec.Decode(&m); err == io.EOF {
break
} else if err != nil {
log.Fatal(err)
}
fmt.Printf("%s: %s\n", m.Name, m.Text)
}
}

Answer 4

Passing a value in quotation marks make that look like string. Change "price":"3460.00" to "price":3460.00 and everything works fine.
If you can't drop the quotations marks you have to parse it by yourself, using strconv.ParseFloat:
package main
import (
"encoding/json"
"fmt"
"strconv"
)
type Product struct {
Name string
Price string
PriceFloat float64
}
func main() {
s := `{"name":"Galaxy Nexus", "price":"3460.00"}`
var pro Product
err := json.Unmarshal([]byte(s), &pro)
if err == nil {
pro.PriceFloat, err = strconv.ParseFloat(pro.Price, 64)
if err != nil { fmt.Println(err) }
fmt.Printf("%+v\n", pro)
} else {
fmt.Println(err)
fmt.Printf("%+v\n", pro)
}
}