golang json converts int to float. What can i do

Question

Here is my code. I'm reading from a JSON file and want to insert the value into my global variable mode.

    jsonFile, err := os.Open("config.json")
if err != nil {
    log.Fatal(err)
    return err
}
//byteValue, _ := ioutil.ReadAll(jsonFile)

var responseJson map[string]interface{}
/*if err := json.NewDecoder(jsonFile).Decode(&responseJson); err != nil {
    log.Fatal(err)
    return err
}*/
d := json.NewDecoder(jsonFile)
d.UseNumber()
d.Decode(&responseJson)
mode = responseJson["mode"].(int)

Type-assert `float64`, and convert it to `int`. Or use a struct to model your JSON, where you can use `int` type for the field. — icza, Mar 18 '22 at 10:29
Please, give an example of the code that follows the [MRE](https://stackoverflow.com/help/minimal-reproducible-example), that is a way for a reader to copy/paste your code, and get the same issue. — RafazZ, Mar 19 '22 at 05:42

score 4 · Answer 1 · answered Mar 18 '22 at 10:55

Type-assert with conversion:

var json_file = bytes.NewReader([]byte(`{"mode":1234}`))

func main() {
    var responseJson map[string]interface{}
    d := json.NewDecoder(json_file)
    if err := d.Decode(&responseJson); err != nil {
        panic(err)
    }
    mode := int(responseJson["mode"].(float64))
    fmt.Println(mode)
}

Type-assert with json.Number

var json_file = bytes.NewReader([]byte(`{"mode":1234}`))

func main() {
    var responseJson map[string]interface{}
    d := json.NewDecoder(json_file)
    d.UseNumber()
    if err := d.Decode(&responseJson); err != nil {
        panic(err)
    }
    i64, err := (responseJson["mode"].(json.Number)).Int64()
    if err != nil {
        panic(err)
    }
    mode := int(i64)
    fmt.Println(mode)
}

With struct:

var json_file = bytes.NewReader([]byte(`{"mode":1234}`))

func main() {
    var responseJson struct{ Mode int }
    d := json.NewDecoder(json_file)
    if err := d.Decode(&responseJson); err != nil {
        panic(err)
    }
    fmt.Println(responseJson.Mode)
}

note how simple that `struct` implementation is @BigBoy. all the type handling is done for you, which is why I nearly always decode json into a struct — erik258, Mar 18 '22 at 19:08

golang json converts int to float. What can i do

1 Answers1