I'm trying to get a value from a JSON and cast it to int but it doesn't work, and I don't know how to do it properly.
Here is the error message:
...cannot convert val (type interface {}) to type int: need type assertion
And the code:
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
Instead of
iAreaId := int(val)
you want a type assertion:
iAreaId := val.(int)
iAreaId, ok := val.(int) // Alt. non panicking version
The reason why you cannot convert an interface typed value are these rules in the referenced specs parts:
Conversions are expressions of the form
T(x)
whereT
is a type andx
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.
But
iAreaId := int(val)
is not any of the cases 1.-7.