CODEWITHSUNDEEP
c++qtvalgrindqlayout
ChrizZlyBear
ChrizZlyBear

Reputation: 193

CLion shows a memory leakage warning when creating Qt Layouts

I have this (minimal example) code in my mainwindow.cpp:

MainWindow::MainWindow(QWidget *parent) :
    QWidget(parent) {
    setWindowTitle("Drawing Window");
    setFixedSize(800, 600);
    
    auto *layout = new QVBoxLayout(this);
    auto *hlayout = new QHBoxLayout();
    
    // Create the Button
    button = new QPushButton("Load Image", this);
    button->setGeometry(10, 10, 80, 30);
    
    // Create the drawing area
    drawingArea = new QLabel(this);
    drawingArea->setFixedSize(512, 512);
    
    layout->addWidget(button);
    hlayout->addWidget(drawingArea);
    layout->addLayout(hlayout);
}

main.cpp:

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
    MainWindow window;
    window.show();
    return app.exec();
}

From what I understand, Qt should handle the memory of my layouts by itself, due to the parent-child relations.

However: CLion shows the warning Allocated memory is leaked in the lines:

auto *layout = new QVBoxLayout(this);
auto *hlayout = new QHBoxLayout();

Running this code with Valgrind, I get the following warnings:

Leak_DefinetlyLost - 2 Warnings
Leak_PossiblyLost - 136 Warnings
UninitCondition - 209 Warnings

Is there an issue with my code? Should I delete my Layouts in the destructor? Why? Doesn't Qt handle this for me?

Upvotes: 6

Views: 276

Answers (1)

Alexander
Alexander

Reputation: 85

Following the advice of Sir Nate, we can found that in your example layout does not have a parent. The problem here is that

QMainWindow objects come with their own customized layout and setting a layout on a the actual main window, or creating a layout with a main window as a parent, is considered an error. You should always set your own layout on the central widget instead.

as stated at Qt official Menus Example in section called "MainWindow Class Implementation".

As a result, when you create QVBoxLayout with this argument it fails to set parent for layout. Thus, neither the layout nor its child hlayout will be deleted.

To achieve proper memory management you should create and set a central widget for main window and then add layout into it. You can also find code example at the link above.

Upvotes: 1

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