如何使用类型转换将 JSON 从 string 解码为 float64

我需要用浮点数解码一个 JSON 字符串，比如:

{"name":"Galaxy Nexus", "price":"3460.00"}

我使用下面的 Golang 代码:

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)
}
}

当我运行它时，得到结果:

json: cannot unmarshal string into Go value of type float64
{Name:Galaxy Nexus Price:0}

我想知道如何解码类型转换的 JSON 字符串。

86183 次浏览
小开

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)
}
}
小开
最佳答案

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)
}
}
小开

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)
}
小开

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)
}
}

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