Hi,

I'm using this method to change the position of 2 widgets placed in a grid layout, I took the code from https://stackoverflow.com/questions/...d-layout-items

Qt Code: 
  1. void MyApp::swapWidgets(QGridLayout* grid, QWidget* widgetA, QWidget *widgetB)
  2. {
  3.     if (!grid)
  4.     {
  5.         return;
  6.     }
  7.  
  8.     int indexA = grid->indexOf(widgetA);
  9.     int indexB = grid->indexOf(widgetB);
  10.     int row1, column1, rowSpan1, columnSpan1;
  11.     int row2, column2, rowSpan2, columnSpan2;
  12.  
  13.     grid->getItemPosition(indexA, &row1, &column1, &rowSpan1, &columnSpan1);
  14.     grid->getItemPosition(indexB, &row2, &column2, &rowSpan2, &columnSpan2);
  15.  
  16.     grid->takeAt(indexA);
  17.     grid->takeAt(indexB);
  18.  
  19.     grid->addWidget(widgetB, row1, column1, rowSpan1, columnSpan1);
  20.     grid->addWidget(widgetA, row2, column2, rowSpan2, columnSpan2);
  21. }
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All my widgets belong to the auto-generated GUI class (from the UI file).

I ran Valgrind and I noticed leaks when this function gets called, the number of leaks is strangely lower than the calls to the swapWidgets method :

==24440== 88 bytes in 1 blocks are definitely lost in loss record 11,181 of 15,003
==24440== at 0x4C2A1E3: operator new(unsigned long) (vg_replace_malloc.c:334)
==24440== by 0x1E8BA469: QLayoutPrivate::createWidgetItem(QLayout const*, QWidget*) (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440== by 0x1E8B95F0: QGridLayout::addWidget(QWidget*, int, int, int, int, QFlags<Qt::AlignmentFlag>) (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440== by 0x4AA313: Ui_MyApp::setupUi(QWidget*) (==24440== 88 bytes in 1 blocks are definitely lost in loss record 11,181 of 15,003
==24440== at 0x4C2A1E3: operator new(unsigned long) (vg_replace_malloc.c:334)
==24440== by 0x1E8BA469: QLayoutPrivate::createWidgetItem(QLayout const*, QWidget*) (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440== by 0x1E8B95F0: QGridLayout::addWidget(QWidget*, int, int, int, int, QFlags<Qt::AlignmentFlag>) (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440== by 0x4AA313: Ui_MyApp::setupUi(QWidget*) (ui_MyApp.h:997)
==24440== by 0x47D361: MyApp::MyApp(QWidget*) (MyApp.cpp:89)
==24440== by 0x47AA51: main (main.cpp:36)
==24440== .h:997)
==24440== by 0x47D361: MyApp::MyApp(QWidget*) (MyApp.cpp:89)
==24440== by 0x47AA51: main (main.cpp:36)
==24440==
==24440== 88 bytes in 1 blocks are definitely lost in loss record 11,182 of 15,003
==24440== at 0x4C2A1E3: operator new(unsigned long) (vg_replace_malloc.c:334)
==24440== by 0x1E8BA469: QLayoutPrivate::createWidgetItem(QLayout const*, QWidget*) (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440== by 0x1E8B95F0: QGridLayout::addWidget(QWidget*, int, int, int, int, QFlags<Qt::AlignmentFlag>) (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440== by 0x49746D: MyApp::swapWidgets(QGridLayout*, QWidget*, QWidget*) (MyApp.cpp:3765)
==24440== by 0x4807E8: MyApp::ConnectSignalsSlots()::{lambda(bool)#15}:perator()(bool) const (MyApp.cpp:758)
==24440== by 0x49ACF8: QtPrivate::FunctorCall<QtPrivate::IndexesList<0>, QtPrivate::List<bool>, void, MyApp::ConnectSignalsSlots()::{lambda(bool)#15}>:: call({lambda(bool)#15}&, void**) (qobjectdefs_impl.h:130)
==24440== by 0x49A82C: void QtPrivate::Functor<MyApp::ConnectSignalsSlots()::{ lambda(bool)#15}, 1>::call<QtPrivate::List<bool>, void>({lambda(bool)#15}&, void*, {lambda(bool)#15}&*) (qobjectdefs_impl.h:240)
==24440== by 0x49A3DB: QtPrivate::QFunctorSlotObject<MyApp::ConnectSignal sSlots()::{lambda(bool)#15}, 1, QtPrivate::List<bool>, void>::impl(int, QtPrivate::QSlotObjectBase*, QObject*, void**, bool*) (qobject_impl.h:168)
==24440== by 0x1F4DB8B2: QMetaObject::activate(QObject*, int, int, void**) (in /usr/lib64/libQt5Core.so.5.9.2)
==24440== by 0x1E994F41: QAbstractButton::clicked(bool) (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440== by 0x1E995179: ??? (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440== by 0x1E996732: ??? (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440==
==24440== 88 bytes in 1 blocks are definitely lost in loss record 11,183 of 15,003
==24440== at 0x4C2A1E3: operator new(unsigned long) (vg_replace_malloc.c:334)
==24440== by 0x1E8BA469: QLayoutPrivate::createWidgetItem(QLayout const*, QWidget*) (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440== by 0x1E8B95F0: QGridLayout::addWidget(QWidget*, int, int, int, int, QFlags<Qt::AlignmentFlag>) (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440== by 0x4974A4: MyApp::swapWidgets(QGridLayout*, QWidget*, QWidget*) (MyApp.cpp:3766)
==24440== by 0x4807E8: MyApp::ConnectSignalsSlots()::{lambda(bool)#15}:perator()(bool) const (MyApp.cpp:758)
==24440== by 0x49ACF8: QtPrivate::FunctorCall<QtPrivate::IndexesList<0>, QtPrivate::List<bool>, void, MyApp::ConnectSignalsSlots()::{lambda(bool)#15}>:: call({lambda(bool)#15}&, void**) (qobjectdefs_impl.h:130)
==24440== by 0x49A82C: void QtPrivate::Functor<MyApp::ConnectSignalsSlots()::{ lambda(bool)#15}, 1>::call<QtPrivate::List<bool>, void>({lambda(bool)#15}&, void*, {lambda(bool)#15}&*) (qobjectdefs_impl.h:240)
==24440== by 0x49A3DB: QtPrivate::QFunctorSlotObject<MyApp::ConnectSignal sSlots()::{lambda(bool)#15}, 1, QtPrivate::List<bool>, void>::impl(int, QtPrivate::QSlotObjectBase*, QObject*, void**, bool*) (qobject_impl.h:168)
==24440== by 0x1F4DB8B2: QMetaObject::activate(QObject*, int, int, void**) (in /usr/lib64/libQt5Core.so.5.9.2)
==24440== by 0x1E994F41: QAbstractButton::clicked(bool) (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440== by 0x1E995179: ??? (in /usr/lib64/libQt5Widgets.so.5.9.2)
==24440== by 0x1E996732: ??? (in /usr/lib64/libQt5Widgets.so.5.9.2)
What can I change in swapWidgets() to fix that leak ?

The first leak above, shows that the GUI object (autogeneratged) is no longer the owner of something (QGridLayout or QWidget, I dunno) manipulated by swapWidgets.