将 interface{} 转换为 int

Question

我正在尝试从 JSON 中获取一个值并将其转换为 int 但它不起作用，我不知道如何正确执行。这是错误消息：...cannot convert val (type interface {}) to type int: need type assertion和代码：    var f interface{}    err = json.Unmarshal([]byte(jsonStr), &f)    if err != nil {        utility.CreateErrorResponse(w, "Error: failed to parse JSON data.")        return    }    m := f.(map[string]interface{})    val, ok := m["area_id"]    if !ok {        utility.CreateErrorResponse(w, "Error: Area ID is missing from submitted data.")        return    }    fmt.Fprintf(w, "Type = %v", val)   // <--- Type = float64    iAreaId := int(val)                // <--- Error on this line.    testName := "Area_" + iAreaId      // not reaching here

Answer 1

我假设：如果您通过浏览器发送 JSON 值，那么您发送的任何数字都将是 float64 类型，因此您无法在 golang 中直接获取该值。

所以做这样的转换：

//As that says: 

fmt.Fprintf(w, "Type = %v", val) // <--- Type = float64

var iAreaId int = int(val.(float64))

这样你就可以得到你想要的确切价值。

Answer 2

添加另一个使用的答案switch......那里有更全面的例子，但这会给你这个想法。

例如，t成为每个case范围内的指定数据类型。请注意，您必须case在一个类型中仅提供一种类型，否则t仍然是interface.

package main

import "fmt"

func main() {

    var val interface{} // your starting value

    val = 4

    var i int // your final value

    switch t := val.(type) {

    case int:

        fmt.Printf("%d == %T\n", t, t)

        i = t

    case int8:

        fmt.Printf("%d == %T\n", t, t)

        i = int(t) // standardizes across systems

    case int16:

        fmt.Printf("%d == %T\n", t, t)

        i = int(t) // standardizes across systems

    case int32:

        fmt.Printf("%d == %T\n", t, t)

        i = int(t) // standardizes across systems

    case int64:

        fmt.Printf("%d == %T\n", t, t)

        i = int(t) // standardizes across systems

    case bool:

        fmt.Printf("%t == %T\n", t, t)

        // // not covertible unless...

        // if t {

        //  i = 1

        // } else {

        //  i = 0

        // }

    case float32:

        fmt.Printf("%g == %T\n", t, t)

        i = int(t) // standardizes across systems

    case float64:

        fmt.Printf("%f == %T\n", t, t)

        i = int(t) // standardizes across systems

    case uint8:

        fmt.Printf("%d == %T\n", t, t)

        i = int(t) // standardizes across systems

    case uint16:

        fmt.Printf("%d == %T\n", t, t)

        i = int(t) // standardizes across systems

    case uint32:

        fmt.Printf("%d == %T\n", t, t)

        i = int(t) // standardizes across systems

    case uint64:

        fmt.Printf("%d == %T\n", t, t)

        i = int(t) // standardizes across systems

    case string:

        fmt.Printf("%s == %T\n", t, t)

        // gets a little messy...

    default:

        // what is it then?

        fmt.Printf("%v == %T\n", t, t)

    }

    fmt.Printf("i == %d\n", i)

}