How to sent a function as an argument to a function c++ qt?

RuWex

Hi:)
I have this function:

{statusBar()->showMessage(tr("Ready Start Testing"), 2000);}

and I want t sent it as argument to that function:

void ShowMessage(----here get the function -----)
{
        function()
}

my questions is:
How to declare the function?
how to get it in the function??
thank!!

JonB

@RuWex
One way is to use std::function(). There are many examples, such as https://www.codingame.com/playgrounds/15869/c-runnable-snippets/passing-a-function-as-parameter or https://stackoverflow.com/a/52602922/489865 or https://stackoverflow.com/a/66224676/489865.

One answer from 2011 --- I don't know if there are better ways now or if this still works --- at https://stackoverflow.com/a/6458710/489865 just boils down to:

template<typename Functor>
void f(Functor functor)
{
   cout << functor(10) << endl;
}

int main() 
{
    auto lambda = [] (int x) { cout << x * 50 << endl; return x * 100; };
    f(lambda); //pass lambda
}

which you can adapt to your case? Might be as simple as:

template<typename Functor>
void ShowMessage(Functor functor)
{
    functor();
}

    auto lambda = [=] () { statusBar()->showMessage(tr("Ready Start Testing"), 2000); };
    ShowMessage(lambda); //pass lambda

?

RuWex

@JonB
I did it ,
But its make problem:(
look:

auto showMessageTime=[]() {statusBar()->showMessage(tr("Testing"), 2000);};

and its make this Error:
C:\Projects\mainwindow.cpp:138: error: cannot call member function 'QStatusBar* QMainWindow::statusBar() const' without object
Do you know why?

JonB

@RuWex said in How to sent a function as an argument to a function c++ qt?:

Do you know why?

Yes, because you didn't copy what I pasted. If you do, it will work. You decided to make a change to it, and took out something I had deliberately put in.

SimonSchroeder

@RuWex said in How to sent a function as an argument to a function c++ qt?:

C:\Projects\mainwindow.cpp:138: error: cannot call member function 'QStatusBar* QMainWindow::statusBar() const' without object
Do you know why?

The error is quite clear. statusBar() needs to be called on a QMainWindow object. Have a look at your lambda captures and think about implicit this in method calls.