c++ - How to control the copy of return object into a new object? -

-

This code is overloaded in order to control operator behavior for the operator = class A objects, and the copy constructor was also declared to see that it was used for the copy process.

My question is, the compiler, a_object + b_object in c_object if the copy constructor and assignment operator was not used as shown in the output ? And in this case how to control the copy behavior? 

  #include & lt; Iostream & gt; #deleted panellines (x) std :: cout & lt; & Lt; X & lt; & Lt; "---------------------------- \ n"; Class A {IIT value; Public: A (Int V = 0): Value (v) {} A (Constant A and A) {std :: cout & lt; & Lt; "CUSTOM CREATOR ... \ n"; Value = a.value; } Consta and A. Operator = (Constant A & A) {std :: cout & lt; & Lt; "= Operator ... \ n"; This- & gt; Value = a.value; Return * This; } Const. One operator + (Constant A & A) {Return A (Value + A. Value); } Zero print (std :: ostream & os) {OS & lt; & Lt; Price & lt; & Lt; Std :: endl; }}; Int main () {one a_object (10); A b_object (20); PUTLINE (1); One c_object = a_object + b_object; // What does the compiler do to make this copy? PUTLINE (2); A d_object = c_object; PUTLINE (3); C_object.print (std :: court); PUTLINE (4); D_object.print (std :: court); PUTLINE (5); A_object = c_object; PUTLINE (6); A_object.print (std :: court); }

Outputs look like this: 

  1 --------------------- - ------ 2 ---------------------------- Copy creator ... 3 -------- - ------------------- 30 4 ---------------------------- 30 5 ---------------------------- = Operator ... 6 --------------  
 Experience and in some situations, the compiler is allowed to create a blank object directly in the destination, copy it by making it temporary.  
 It's okay what's going on in your case: return value  operator +  to  c_object  in the space  (int)  Constructor is created, so you will not see the call to the copy constructor. 
 
 With GCC, you can pass the command-line flag  -fno-elide-constructors , which prevents the copy elision. You will then see all the copy creator calls. .

Comments

Post a Comment

Popular posts from this blog

c# - SignalR: "Protocol error: Unknown transport." when navigating to hub -

-
Image
I am trying to use the ASP.NET signal for the first time - here's what I did: created a new web Has been added to the project and the following signal R packages: I have created the following category: [Hub-name ("chat")] Public class ChatHub: Hub {Public Zero Halo () {Clients.All.hello ( ); }} and the following startup configuration: public partial class startup {public zero configuration (IAppBuilder app) {configure (app); App.MapSignalR (); }} However, whenever I navigate localhost: (port) / api / signalr / chat I get the following error: Protocol error: Unknown transport. I am running a new browser and trying different people so remove it from the API / URL, and just use the localhost: (potter) / signaller / Chat
Read more

c# - WPF Expander overlay used in ItemsControl -

-
I've been searching for a while, but all the solutions I can only deal with parts of my issue. With an item control, which includes the expansion, upon expansion, the content of the extensioner should be shown as an item which is overlapping the other item in the item control and not taking them down. The following XAML-code is actually a big problem: the content of the expansion does not overlap other objects but is hidden behind them, I think it is because of ZIndex because the following in ItemsControl Items are added after expander content. I managed to set a single spreader's ZIndex 99 style triggers, but it appears to be very complicated and error-prone solution any thoughts? & lt; Window x: orbit = "wpfTest.MainWindow" xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns: x = "http://schemas.microsoft.com/winfx/2006/ Xaml "title =" main window "height =" 350 "width =" 525 "...
Read more

class - Kivy: how to instantiate a dynamic classes in python -

-
Using KV lang on my Python code, I have taken a hard time trying to instantiate a dynamic class, the following Consider the code: My test.kv file looks like this: & lt; MyPopup @ popup: Title: 'Hello' size_hunt: (1, .6) Grid layout: ID: RouteGrid column: 2 padding: ['8dp', '4dp', '8dp', '4dp'] Difference: '8dp' label: text: 'some text here' button: text: 'OK' On_press: do_something () & lt; MyGrid & gt;: Rows: 1 Button: Text: 'Show Popup' on_press: root.pop.show () Then import Kivy.app into my test.py: I get the following error: raise Factory Exception ('Uncount Class' '% name) kivy.factory.FactoryException: Unknown class Can anyone tell me how to do this properly, what do I remember? If you need more information please let me know Thank you. Takes a call to the factory before the KV file is loaded, so you want the class to Are not yet in existence. As long as no clas...
Read more