CODEWITHSUNDEEP
c++timeoutgtkgtkmm
JesseL
JesseL

Reputation: 21

Creating a timeout method in a gtkmm app causes "void value not ignored as it ought to be" error

I have just gotten started with gtkmm and I am trying to update a label at a predefined interval by letting a timeout method call my Update() method. However, when writing the following line in the constructor of my MainWindow class:

Glib::signal_timeout().connect(sigc::mem_fun(*this, &MainWindow::Update), 1000);

I get the following error:

/usr/include/sigc++-2.0/sigc++/functors/slot.h:136:36: error: void value not ignored as it ought to be return (typed_rep->functor_)();

Does anybody have a clue on how to fix this or what is the cause?

Edit: Here is a minimal and reproducible example:

main.ccp

#include <gtkmm.h>
#include "MainWindow.h"

int main(int argc, char* argv[])
{
    auto app = Gtk::Application::create(argc, argv, "com.companyname.test");

    Glib::RefPtr<Gtk::Builder> builder = Gtk::Builder::create_from_file("prototype.glade");

    MainWindow* mainWindow = 0;
    builder->get_widget_derived("mainWindow", mainWindow);

    return app->run(*mainWindow);
}

MainWindow.h

#pragma once
#include <gtkmm.h>

class MainWindow : public Gtk::Window
{
public:
    MainWindow(BaseObjectType* cobject, const Glib::RefPtr<Gtk::Builder>& refGlade);
    virtual ~MainWindow();

protected:
    //Signal handlers:
    void Update();
};

MainWindow.cpp

#include "MainWindow.h"
#include <iostream>

MainWindow::MainWindow(BaseObjectType* cobject, const Glib::RefPtr<Gtk::Builder>& refGlade)
{
    // The following line creates "void value not ignored as it ought to be (...)" error
    Glib::signal_timeout().connect(sigc::mem_fun(*this, &MainWindow::Update), 1000);
}

MainWindow::~MainWindow()
{

}

void MainWindow::Update()
{
    
    std::cout << "Update" << std::endl;
}

Upvotes: 1

Views: 325

Answers (1)

JesseL
JesseL

Reputation: 21

As Scheff mentioned in the comments, I forgot that MainWindow::Update needs to return a value of type bool, as that is expected by signal_timeout. Changing the Update method to the following, fixed the issue:

bool MainWindow::Update()
{
    
    std::cout << "Update" << std::endl;
    
    return true;
}

Upvotes: 1

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