带有长数字的JSON解组可提供浮点数 [英] JSON unmarshaling with long numbers gives floating point number

问题描述

我正在使用golang编组和解组JSON，例如，当我想对数字字段进行编组时，golang会将其转换为浮点数而不是使用长数.

I was marshaling and unmarshaling JSONs using golang and when I want to do it with number fields golang transforms it in floating point numbers instead of use long numbers, for example.

我有以下JSON:

{
    "id": 12423434, 
    "Name": "Fernando"
}

在marshal之后将其映射到地图，然后将unmarshal再次转换为json字符串:

After marshal it to a map and unmarshal again to a json string I get:

{
    "id":1.2423434e+07,
    "Name":"Fernando"
}

如您所见，"id"字段采用浮点表示法.

As you can see the "id" field is in floating point notation.

我正在使用的代码如下:

The code that I am using is the following:

package main

import (
    "encoding/json"
    "fmt"
    "os"
)

func main() {

    //Create the Json string
    var b = []byte(`
        {
        "id": 12423434, 
        "Name": "Fernando"
        }
    `)

    //Marshal the json to a map
    var f interface{}
    json.Unmarshal(b, &f)
    m := f.(map[string]interface{})

    //print the map
    fmt.Println(m)

    //unmarshal the map to json
    result,_:= json.Marshal(m)

    //print the json
    os.Stdout.Write(result)

}

它打印:

map[id:1.2423434e+07 Name:Fernando]
{"Name":"Fernando","id":1.2423434e+07}

似乎是地图的第一个marshal生成了FP.我该如何解决呢?

It appears to be that the first marshal to the map generates the FP. How can I fix it to a long?

这是goland游乐场中程序的链接: http://play.golang.org/p/RRJ6uU4Uw-

This is the link to the program in the goland playground: http://play.golang.org/p/RRJ6uU4Uw-

推荐答案

有时您无法预先定义结构，但仍要求数字不变地通过编组-解组过程.

There are times when you cannot define a struct in advance but still require numbers to pass through the marshal-unmarshal process unchanged.

在这种情况下，您可以在json.Decoder上使用UseNumber方法，这将导致所有数字都以json.Number的形式编组(这只是数字的原始字符串表示形式).这对于在JSON中存储很大的整数也很有用.

In that case you can use the UseNumber method on json.Decoder, which causes all numbers to unmarshal as json.Number (which is just the original string representation of the number). This can also useful for storing very big integers in JSON.

例如:

package main

import (
    "strings"
    "encoding/json"
    "fmt"
    "log"
)

var data = `{
    "id": 12423434, 
    "Name": "Fernando"
}`

func main() {
    d := json.NewDecoder(strings.NewReader(data))
    d.UseNumber()
    var x interface{}
    if err := d.Decode(&x); err != nil {
        log.Fatal(err)
    }
    fmt.Printf("decoded to %#v\n", x)
    result, err := json.Marshal(x)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Printf("encoded to %s\n", result)
}

结果:

decoded to map[string]interface {}{"id":"12423434", "Name":"Fernando"}
encoded to {"Name":"Fernando","id":12423434}

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