将interface {}转换为int在Golang

发布时间：2020-12-16 18:05:42 所属栏目：大数据来源：网络整理

导读：我刚刚接触Golang，我试图从JSON中获取值并将其转换为int，但它不工作。不知道如何正确地做。这里是错误消息： ...cannot convert val (type interface {}) to type int: need type assertion 代码： var f interface{} err = json.Unmarshal([]byte(jsonSt

我刚刚接触Golang，我试图从JSON中获取值并将其转换为int，但它不工作。不知道如何正确地做。

这里是错误消息：

...cannot convert val (type interface {}) to type int: need type assertion

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

任何帮助将不胜感激。

代替

iAreaId := int(val)

你想要一个type assertion：

iAreaId := val.(int)
iAreaId,ok := val.(int) // Alt. non panicking version

为什么你不能convert一个接口类型的值的原因是引用规范部分中的这些规则：

Conversions are expressions of the form T(x) where T is a type and x is an expression that can be converted to type T.

… …

A non-constant value x can be converted to type T in any of these cases:

x is assignable to T.

x’s type and T have identical underlying types.

x’s type and T are unnamed pointer types and their pointer base types have identical underlying types.

x’s type and T are both integer or floating point types.

x’s type and T are both complex types.

x is an integer or a slice of bytes or runes and T is a string type.

x is a string and T is a slice of bytes or runes.

但

iAreaId := int(val)

不是任何一种情况1.-7。

（编辑：李大同）

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