c++ - an enclosing-function local variable cannot be referenced in a lambda body unless if it is in capture list -

I have the json :: value object and I try to get the value in a straight but I'm about the capture list I get this error in I understand that this bracket holds the [] capture list in the phrase, but I can not understand how I can return a value in the Lambda function?

  Zero Jasondomain :: Set Value (JSN :: Value OBG) {weather.coord.lon = obj.at (L "Coordination"). (L "longitude") as_double () .; Weather.coord.lat = obj.at (L "Coordinate"). (L "Latitude"). As_double (); } Zero JsonDeneme :: getHttp () {// json :: value val; Http_client Client (U ("http://api.openweathermap.org/data/2.5/weather?q=Ankara,TR")); Client.request (methods :: GET) .then ([] (http_response response) - & gt; pplx :: task & lt; json :: value & gt; {if (response.status_code) == condition_code :: OK ) {Printf ("Received response status code:% u \ n", response.status_code ()); Return response .extract_json ();} return pplx :: task_from_result (json :: value ());}). Then ([] (PPLX: Work:  PreviousTask) {try {json :: value v = previousTask.get (); Set value (v); // ------ ------------ -----------------------} (http_exception const & amp; a) {wcout & lt; & Lt; e.what () & lt; endl;}}) .Request (); }  

The capture-list that you put in the middle of the square bracket See:

  void foo () {int i = 0; [] () {I + = 2; }}  

Here Lambda does not capture anything, thus it will not reach the enclosed area, and it will not know what is i now, Capture everything from the context:

  void foo () {int i = 0; [& Amp;] () // Note & amp ;. This means that we are capturing all the attached variables of reference {i + = 2; } Cout & lt; & Lt; 2; }  

In this example, the reference in the attached area to the i inside the lambda is i .

In your example, you have a lambda within a member- the function of an object. You are trying to call the object's function: setValues ​​(v) , but your capture list is empty, so your lambda does not know that setValues ​​ Now, if you capture this in Lambda, then Lambda will have access to all the objects of the object, because setValues ​​(v) is similar < Code> this- & gt; Set Value (v) In your case, the error will end.