Destroying json array in delphi-CodePudding

The code below creates a memory leak. What is the correct method?

  JSONArray := TJSONArray.Create;
  try
    JSONArray :=
      TJSONObject.ParseJSONValue(
        TEncoding.UTF8.GetBytes(
          '[{"username":"admin"},{"username":"developer"}]'
        ), 0
      ) as TJSONArray;
  finally
    JSONArray.Free;
  end;

CodePudding user response：

The problem is the call to TJSONArray.Create. You are creating your own TJSONArray object, then overwriting the JSONArray pointer to point at a completely different TJSONArray object, leaking the original object you Create'd.

So, simply get rid of that Create call, you don't need it. You need to Free only the object that ParseJSONValue() returns.

Also, you don't need to convert the JSON string to bytes. ParseJSONValue() has an overload that accepts a string as input.

Try this:

JSONArray := TJSONObject.ParseJSONValue(
  '[{"username":"admin"},{"username":"developer"}]'
) as TJSONArray;
try
  // ...
finally
  JSONArray.Free;
end;

CodePudding user response：

Just as an alternative to the valid provided solution, but using mORMot. IMHO simpler, cleaner and avoiding memory leaks:

program Project1;

{$APPTYPE CONSOLE}

uses
  Syncommons;

var Json : TDocVariantData;
begin
  Json.InitJSon('[{"username":"admin"},{"username":"developer"}]');
  // Testing
  assert(Json.Kind = dvArray);
  assert(Json.Count = 2);
  assert(TDocVariantData(Json.Values[1]).U['username'] = 'developer');
end.

Please, find further details and alternatives in the amazing documentation.