如何将字符串转换为float64类型并解码JSON

huangapple
go评论116阅读模式
英文:

How to decode JSON with type convert from string to float64

问题

我需要解码一个包含浮点数的JSON字符串，例如：

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

我使用以下的Golang代码：

  1. package main
  3. import (
  4.     "encoding/json"
  5.     "fmt"
  6. )
  8. type Product struct {
  9.     Name  string
  10.     Price float64
  11. }
  13. func main() {
  14.     s := `{"name":"Galaxy Nexus", "price":"3460.00"}`
  15.     var pro Product
  16.     err := json.Unmarshal([]byte(s), &pro)
  17.     if err == nil {
  18.         fmt.Printf("%+v\n", pro)
  19.     } else {
  20.         fmt.Println(err)
  21.         fmt.Printf("%+v\n", pro)
  22.     }
  23. }

当我运行它时，得到的结果是：

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

我想知道如何进行类型转换来解码JSON字符串。

英文:

I need to decode a JSON string with the float number like:

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

I use the Golang code below:

  1. package main
  3. import (
  4.     "encoding/json"
  5.     "fmt"
  6. )
  8. type Product struct {
  9.     Name  string
  10.     Price float64
  11. }
  13. func main() {
  14.     s := `{"name":"Galaxy Nexus", "price":"3460.00"}`
  15.     var pro Product
  16.     err := json.Unmarshal([]byte(s), &pro)
  17.     if err == nil {
  18. 	    fmt.Printf("%+v\n", pro)
  19.     } else {
  20. 	    fmt.Println(err)
  21. 	    fmt.Printf("%+v\n", pro)
  22.     }
  23. }

When I run it, get the result:

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

I want to know how to decode the JSON string with type convert.

答案1

得分: 221

答案相对简单。只需告诉JSON解释器它是一个编码为float64的字符串，使用,string（请注意，我只改变了Price的定义）：

  1. package main
  3. import (
  4.     "encoding/json"
  5.     "fmt"
  6. )
  8. type Product struct {
  9.     Name  string
  10.     Price float64 `json:",string"`
  11. }
  13. func main() {
  14.     s := `{"name":"Galaxy Nexus", "price":"3460.00"}`
  15.     var pro Product
  16.     err := json.Unmarshal([]byte(s), &pro)
  17.     if err == nil {
  18.         fmt.Printf("%+v\n", pro)
  19.     } else {
  20.         fmt.Println(err)
  21.         fmt.Printf("%+v\n", pro)
  22.     }
  23. }
英文:

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):

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. )
  8. type Product struct {
  9. 	Name  string
  10. 	Price float64 `json:",string"`
  11. }
  13. func main() {
  14. 	s := `{"name":"Galaxy Nexus", "price":"3460.00"}`
  15. 	var pro Product
  16. 	err := json.Unmarshal([]byte(s), &pro)
  17. 	if err == nil {
  18. 		fmt.Printf("%+v\n", pro)
  19. 	} else {
  20. 		fmt.Println(err)
  21. 		fmt.Printf("%+v\n", pro)
  22. 	}
  23. }

答案2

得分: 21

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)
}

英文:

Just letting you know that you can do this without Unmarshal and use json.decode. Here is Go Playground

  1. package main
  3. import (
  4.     "encoding/json"
  5.     "fmt"
  6.     "strings"
  7. )
  9. type Product struct {
  10.     Name  string `json:"name"`
  11.     Price float64 `json:"price,string"`
  12. }
  14. func main() {
  15.     s := `{"name":"Galaxy Nexus","price":"3460.00"}`
  16.     var pro Product
  17.     err := json.NewDecoder(strings.NewReader(s)).Decode(&pro)
  18.     if err != nil {
  19. 	    fmt.Println(err)
  20. 	    return
  21.     }
  22.     fmt.Println(pro)
  23. }

答案3

得分: 6

避免将字符串转换为[]byte：b := []byte(s)。它会分配一个新的内存空间，并将整个内容复制到其中。

strings.NewReader 接口更好。下面是来自 godoc 的代码示例：

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. 	"io"
  7. 	"log"
  8. 	"strings"
  9. )
  11. func main() {
  12. 	const jsonStream = `
  13. 	{"Name": "Ed", "Text": "Knock knock."}
  14. 	{"Name": "Sam", "Text": "Who's there?"}
  15. 	{"Name": "Ed", "Text": "Go fmt."}
  16. 	{"Name": "Sam", "Text": "Go fmt who?"}
  17. 	{"Name": "Ed", "Text": "Go fmt yourself!"}
  18. `
  19. 	type Message struct {
  20. 		Name, Text string
  21. 	}
  22. 	dec := json.NewDecoder(strings.NewReader(jsonStream))
  23. 	for {
  24. 		var m Message
  25. 		if err := dec.Decode(&m); err == io.EOF {
  26. 			break
  27. 		} else if err != nil {
  28. 			log.Fatal(err)
  29. 		}
  30. 		fmt.Printf("%s: %s\n", m.Name, m.Text)
  31. 	}
  32. }
英文:

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:

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"fmt"
  6. 	"io"
  7. 	"log"
  8. 	"strings"
  9. )
  11. func main() {
  12. 	const jsonStream = `
  13. 	{"Name": "Ed", "Text": "Knock knock."}
  14. 	{"Name": "Sam", "Text": "Who's there?"}
  15. 	{"Name": "Ed", "Text": "Go fmt."}
  16. 	{"Name": "Sam", "Text": "Go fmt who?"}
  17. 	{"Name": "Ed", "Text": "Go fmt yourself!"}
  18. `
  19. 	type Message struct {
  20. 		Name, Text string
  21. 	}
  22. 	dec := json.NewDecoder(strings.NewReader(jsonStream))
  23. 	for {
  24. 		var m Message
  25. 		if err := dec.Decode(&m); err == io.EOF {
  26. 			break
  27. 		} else if err != nil {
  28. 			log.Fatal(err)
  29. 		}
  30. 		fmt.Printf("%s: %s\n", m.Name, m.Text)
  31. 	}
  32. }

答案4

得分: 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:

  1. package main
  3. import (
  4.     "encoding/json"
  5.     "fmt"
  6.     "strconv"
  7. )
  9. type Product struct {
  10.     Name       string
  11.     Price      string
  12.     PriceFloat float64
  13. }
  15. func main() {
  16.     s := `{"name":"Galaxy Nexus", "price":"3460.00"}`
  17.     var pro Product
  18.     err := json.Unmarshal([]byte(s), &pro)
  19.     if err == nil {
  20.         pro.PriceFloat, err = strconv.ParseFloat(pro.Price, 64)
  21.         if err != nil { fmt.Println(err) }
  22.         fmt.Printf("%+v\n", pro)
  23.     } else {
  24.         fmt.Println(err)
  25.         fmt.Printf("%+v\n", pro)
  26.     }
  27. }
英文:

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:

  1. package main
  3. import (
  4.     "encoding/json"
  5.     "fmt"
  6.     "strconv"
  7. )
  9. type Product struct {
  10.     Name       string
  11.     Price      string
  12.     PriceFloat float64
  13. }
  15. func main() {
  16.     s := `{"name":"Galaxy Nexus", "price":"3460.00"}`
  17.     var pro Product
  18.     err := json.Unmarshal([]byte(s), &pro)
  19.     if err == nil {
  20.         pro.PriceFloat, err = strconv.ParseFloat(pro.Price, 64)
  21.         if err != nil { fmt.Println(err) }
  22.         fmt.Printf("%+v\n", pro)
  23.     } else {
  24.         fmt.Println(err)
  25.         fmt.Printf("%+v\n", pro)
  26.     }
  27. }

huangapple
  • 本文由 发表于 2012年2月26日 20:05:27
  • 转载请务必保留本文链接：https://go.coder-hub.com/9452897.html
  • go
  • json
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