Using more standard library function

[sowas]

hello,
I have a programm from youtube (watch?v=UvUZoS_HaGY) witch is running there, but when try to compile it on my pc, then I get follwing error message std::pair<_T1,_T2>::first has incomplete type.

It is referring to the penultimate line of notesmanager.h.
std::unordered_map<int, std::pair<Note, std::unique_ptr<QTextDocument>>> notes;

I can't find the error, it's because in the .pro file is required c++17.
My pc is running under Kubuntu 20.04, Creator 14.3.2 (Qt 5.15.1)
Does somebody has any idea?
Thanks

the code:
// notes.pro
////////////

QT += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

CONFIG += c++17

You can make your code fail to compile if it uses deprecated APIs.

In order to do so, uncomment the following line.

#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000

disables all the APIs deprecated before Qt 6.0.0

SOURCES +=
main.cpp
mainwindow.cpp
noteslistwidget.cpp
notesmanager.cpp
notewidget.cpp

HEADERS +=
mainwindow.h
note.h
noteslistwidget.h
notesmanager.h
notewidget.h

FORMS +=
mainwindow.ui
noteslistwidget.ui

Default rules for deployment.

qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

// main.cpp
///////////

#include "mainwindow.h"
#include "notesmanager.h"

#include <QApplication>

int main(int argc, char *argv[])
{
QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps, true);
QApplication::setAttribute(Qt::AA_EnableHighDpiScaling,true);

QApplication a(argc, argv);
NotesManager manager;
MainWindow w(manager);

w.show();
return a.exec();

}

//mainwindow.cpp
////////////////

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include "notesmanager.h"
#include "note.h"
#include "noteslistwidget.h"

#include <QPushButton>
#include <QMessageBox>

#include <algorithm>

MainWindow::MainWindow(NotesManager &manager, QWidget *parent)
: QWidget(parent)
, ui(new Ui::MainWindow)
, notesManager(manager)
{
ui->setupUi(this);
makeConnections();
init();
}

MainWindow::~MainWindow()
{
delete ui;
}

void MainWindow::on_newNoteBtn_clicked()
{
notesManager.createNewNote();
}

void MainWindow::on_removeNoteBtn_clicked()
{
removeNote(ui->notesListWidget->currentNoteId());
}

// handle NotesManager signals
void MainWindow::onNewNoteCreated(int id)
{
addNoteToList(notesManager.note(id));
}

void MainWindow::onNoteContentChanged(int id)
{
ui->notesListWidget->updateCurrentNote(notesManager.note(id));
}

// handle NotesListWidget signals
void MainWindow::onSelectedNoteChanged(int id)
{
auto *document = notesManager.noteDocument(id);
if(document)
{
ui->textEdit->setDocument(document);
// auto cursor = ui->textEdit->textCursor();
// cursor.movePosition(QTextCursor::End);
// ui->textEdit->setTextCursor(cursor);
}
}

void MainWindow::onRemoveNote(int id)
{
removeNote(id);
}

void MainWindow::addNoteToList(const Note &note)
{
ui->notesListWidget->addNote(note);
}

void MainWindow::removeNote(int id)
{
QString noteTitle = notesManager.note(id).title;
auto pressedBtn = QMessageBox::information(this,"remove note?",
QString("Are you sure you want to remove %0?").arg(noteTitle),
QMessageBox::Yes|QMessageBox::No,QMessageBox::Yes);

if(pressedBtn == QMessageBox::Yes)
{
    if(notesManager.count() ==1)
        ui->textEdit->setDocument(nullptr);

    ui->notesListWidget->removeCurrentNote();
    notesManager.removeNote(id);
}

}

void MainWindow::init()
{
auto notesList = notesManager.noteCollection();
std::sort(notesList.begin(), notesList.end(),
[](const Note &left, const Note &right)
{
return left.lastModified < right.lastModified;
});
for(auto &note : notesList)
addNoteToList(note);
}

void MainWindow::makeConnections()
{
connect(ui->newNoteBtn, &QPushButton::click, this, &MainWindow::on_newNoteBtn_clicked);
connect(ui->removeNoteBtn, &QPushButton::click, this, &MainWindow::on_removeNoteBtn_clicked);

connect(&notesManager, &NotesManager::newNoteCreated,this, &MainWindow::onNewNoteCreated);
connect(&notesManager, &NotesManager::noteContendChanged, this, &MainWindow::onNoteContentChanged);

connect(ui->notesListWidget, &NotesListWidget::selectedNoteChanged, this, &MainWindow::onSelectedNoteChanged);

}

//MainWindow.h
//////////////

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QWidget>
#include <QPushButton>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class NotesManager;
class Note;

class MainWindow : public QWidget
{
Q_OBJECT

public:
MainWindow(NotesManager &manageNr, QWidget *parent = nullptr);
~MainWindow();

private slots:
// handle signal for ui
void on_newNoteBtn_clicked();
void on_removeNoteBtn_clicked();

// handle NotesManager signals
void onNewNoteCreated(int id);
void onNoteContentChanged(int id);

// handle NotesListWidget signals
void onSelectedNoteChanged(int id);
void onRemoveNote(int id);

private:
void addNoteToList(const Note &note);
void removeNote(int id);

void init();
void makeConnections();
Ui::MainWindow *ui;
NotesManager &notesManager;

};
#endif // MAINWINDOW_H

//mainwindow.ui
///////////////

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>MainWindow</class>
<widget class="QWidget" name="MainWindow">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>800</width>
<height>600</height>
</rect>
</property>
<property name="windowTitle">
<string>MainWindow</string>
</property>
<layout class="QVBoxLayout" name="verticalLayout" stretch="0,1">
<item>
<layout class="QHBoxLayout" name="horizontalLayout">
<item>
<widget class="QPushButton" name="newNoteBtn">
<property name="text">
<string>New</string>
</property>
</widget>
</item>
<item>
<widget class="QPushButton" name="removeNoteBtn">
<property name="text">
<string>Delete</string>
</property>
</widget>
</item>
<item>
<spacer name="horizontalSpacer">
<property name="orientation">
<enum>Qt::Horizontal</enum>
</property>
<property name="sizeHint" stdset="0">
<size>
<width>40</width>
<height>20</height>
</size>
</property>
</spacer>
</item>
</layout>
</item>
<item>
<widget class="QSplitter" name="splitter">
<property name="orientation">
<enum>Qt::Horizontal</enum>
</property>
<property name="childrenCollapsible">
<bool>false</bool>
</property>
<widget class="NotesListWidget" name="notesListWidget" native="true"/>
<widget class="QTextEdit" name="textEdit"/>
</widget>
</item>
</layout>
</widget>
<customwidgets>
<customwidget>
<class>NotesListWidget</class>
<extends>QWidget</extends>
<header>noteslistwidget.h</header>
<container>1</container>
</customwidget>
</customwidgets>
<resources/>
<connections/>
</ui>

//note.h
////////
#pragma once

#include <QString>
#include <QDateTime>

struct Note
{
int id;
QString title;
QString content;
QDateTime lastModified;

};

//noteslistwidget.cpp
///////////////////

#include "noteslistwidget.h"
#include "ui_noteslistwidget.h"

#include "note.h"

NotesListWidget::NotesListWidget(QWidget *parent) :
QWidget(parent),
ui(new Ui::NotesListWidget)
{
ui->setupUi(this);
connect(ui->noteList, &QListWidget::itemSelectionChanged,
this, &NotesListWidget::onItemSlectionChanged);
}

NotesListWidget::~NotesListWidget()
{
delete ui;
}
void NotesListWidget::addNote(const Note &note)
{
auto *item = new QListWidgetItem();
ui->noteList->insertItem(0, item);

setupNoteItem(note, item);

}
void NotesListWidget::removeCurrentNote()
{
auto *currentItem = ui->noteList->currentItem();
if(currentItem != nullptr)
{
delete currentItem;
}
}
void NotesListWidget::updateCurrentNote(const Note &note)
{
if(ui->noteList->currentRow() !=0 )
{
moveCurrenItemToTop(note);
}
}

int NotesListWidget::currentNoteId()
{
auto *currentItem = ui->noteList->currentItem();
int noteId =currentItem->data(Qt::UserRole).toInt();
return noteId;
}

void NotesListWidget::onItemSlectionChanged()
{
auto *currentItem = ui->noteList->currentItem();
if(currentItem)
{
int id = currentNoteId();
emit selectedNoteChanged(id);
}
}
void NotesListWidget::moveCurrenItemToTop(const Note &note)
{
blockSignals(true);
auto *item = ui->noteList->takeItem(ui->noteList->currentRow());

ui->noteList->insertItem(0,item);
setupNoteItem(note, item);
blockSignals(false);

}
void NotesListWidget::setupNoteItem(const Note &note, QListWidgetItem *item)
{
item->setText(note.title);
item->setData(Qt::UserRole, note.id);
ui->noteList->setCurrentItem(item);
}

// notesListWidget.h
////////////////////
#pragma once

#include <QWidget>

namespace Ui {
class NotesListWidget;
}

struct Note;
class QListWidgetItem;

class NotesListWidget : public QWidget
{
Q_OBJECT

public:
explicit NotesListWidget(QWidget *parent = nullptr);
~NotesListWidget();

void addNote(const Note &note);
void removeCurrentNote();
void updateCurrentNote(const Note &note);

int currentNoteId();

signals:
void selectedNoteChanged(int id);

private:
void onItemSlectionChanged();

void moveCurrenItemToTop(const Note &note);
void setupNoteItem(const Note &note, QListWidgetItem *item);

private:
Ui::NotesListWidget *ui;
};

//noteslistwidget.ui
////////////////////

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>NotesListWidget</class>
<widget class="QWidget" name="NotesListWidget">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>261</width>
<height>579</height>
</rect>
</property>
<property name="windowTitle">
<string>Form</string>
</property>
<layout class="QVBoxLayout" name="verticalLayout">
<item>
<widget class="QListWidget" name="noteList"/>
</item>
</layout>
</widget>
<resources/>
<connections/>
</ui>

//notesmanager.cpp
//////////////////

#include "notesmanager.h"
#include "note.h"

#include <QTextDocument>
#include <QSignalMapper>

int nextNoteId();

NotesManager::NotesManager(QObject *parent) : QObject(parent)
{
mapChangedSignalToNoteId = new QSignalMapper(this);
connect(mapChangedSignalToNoteId, &QSignalMapper::mappedInt,
this, &NotesManager::onNoteContentChanged);

readNotes();  

if(notes.size() ==0)
    createNewNote();

}

NotesManager::~NotesManager()
{
writeNotes();
}

void NotesManager::createNewNote()
{
int id = nextNoteId();
auto &[note, textDocument] = notes[id];
note.id = id;
note.title = "new Note";
note.lastModified = QDateTime::currentDateTime();
textDocument = createNewTextDocument(note);

emit newNoteCreated(id);

}

void NotesManager::removeNote(int id)
{
notes.erase(id);

if(notes.empty())
    createNewNote();

}

void NotesManager::renameNote(int id, const QString &newTitle)
{
// todo
// Q_UNUSED(id);
// Q_UNUSED(newTitle);

   auto found = notes.find(id);
   if(found !=notes.end())
   {
       auto &[note, textDocument] = found->second;
       note.title = newTitle;
       note.lastModified = QDateTime::currentDateTime();
   }

}

const Note &NotesManager::note(int id) const
{
return notes.at(id).first;
}

QTextDocument *NotesManager::noteDocument(int id) const
{
auto found = notes.find(id);
if(found != notes.end())
{
return found->second.second.get();
}
return nullptr;
}

std::vector<std::reference_wrapper<Note>>NotesManager::noteCollection()
{
std::vector<std::reference_wrapper<Note>> out;
for(auto &i : notes)
{
auto &[note, QTextDocument] =i.second;
note.content = QTextDocument.toPainText();
out.push_back(note);
}
return out;
}

size_t NotesManager::count() const
{
return notes.size();
}

void NotesManager::onNoteContentChanged(int id)
{
notes.at(id).first.lastModified =QDateTime::currentDateTime();
emit noteContendChanged(id);
}

void NotesManager::readNotes()
{
// todo
}

void NotesManager::writeNotes()
{
// todo
}
std::unique_ptr<QTextDocument> NotesManager::createNewTextDocument(const Note &note)
{
auto textDocument =std::make_unique<QTextDocument>(note.content);
connect(textDocument.get(), &QTextDocument::contentsChange,
mapChangedSignalToNoteId, qOverload<>(&QSignalMapper::map));
mapChangedSignalToNoteId->setMapping(textDocument.get(),note.id);

return textDocument;

}
int nextNoteId()
{
static int id = 0;
return ++id;
}

//notesmanager.h
////////////////

#pragma once
#include <QObject>

#include <unordered_map>
#include <vector>
#include <utility>
#include <memory>

struct Note;

class QTextDocument;
class QSignalMapper;

class NotesManager : public QObject

{
Q_OBJECT
public:
explicit NotesManager(QObject *parent = nullptr);
~NotesManager();

void createNewNote();
void removeNote(int id);
void renameNote(int id, const QString &newTitle);

const Note &note(int id) const;
QTextDocument *noteDocument(int id) const;
std::vector<std::reference_wrapper<Note>> noteCollection();
size_t count() const;

signals:
void newNoteCreated(int id);
void noteContendChanged(int id);

private:
void onNoteContentChanged(int id);
void readNotes();
void writeNotes();
std::unique_ptr<QTextDocument> createNewTextDocument(const Note &note);

private:
std::unordered_map<int, std::pair<Note, std::unique_ptr<QTextDocument>>> notes;
QSignalMapper *mapChangedSignalToNoteId =nullptr;
};

//////////////////////
// end notes.cpp

[sierdzio]

Please use code tags when posting on the forums, otherwise the code is very hard to read:

```
// Some code here
```

You are seeing the error because your notesmanager.h does not include note.h header. You should add:

#include "note.h"

[sowas]

Several errors occurred while copying, the characters "<" and ">" confuse my editor,
parts of functions were assigned incorrectly.

[sierdzio]

@sowas said in Using more standard library function:

Several errors occurred while copying, the characters "<" and ">" confuse my editor,
parts of functions were assigned incorrectly.

What's that got to do with the topic? I don't understand.

Did inclusion of note.h in notesmanager.h solve the problem?

[J.Hilk]

@sowas what version of Qt do you use for your kit? You only posted the one that was used to compile QtCreator.

Depending on the kit, qmake may not know the c++17 command

[sowas]

@J.Hilk
The Kits-Menu

1. Kits
   automatic: Qt 5.12.9 GCC64bit
   Users: (Dektop default)
   C: GCC(C, x86 64bit in /usr/bin/
   C++: GCC9 (C++, x86 64bit in /usr/bin/
   Qt-Version Qt 5.12.8(qt5)

2. Qt-Versions
   automatic: Qt 5.12.9 GCC64bit /home/user/Qt12/5.12.9/gcc_64/bin/qmake.
   user: Qt 5.12.8(qt5) /usr/lib/qt5/bin/qmake

3. Compiler
   Name: Clang(C,x86 64bit in /home/user/Qt15/Tools/QtCreator/libexec/qtcreator/clng/bin)
   Compiler-path: /home/user/Qt15/Tools/QtCreator/libexec/qtcreator/clang/bin/clang

4. Debbuger ...

5. CMake ...

---

According to Creator Info (4.13.2) : Qt 5.15.1 (GCC 5.3.1 20160406 (Red Hat 5.3.1-6),64 bit
readable version of code

now a readable code:

// notes.pro
////////////
QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

CONFIG += c++17

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    
# disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
    main.cpp \
    mainwindow.cpp \
    noteslistwidget.cpp \
    notesmanager.cpp \
    notewidget.cpp

HEADERS += \
    mainwindow.h \
    note.h \
    noteslistwidget.h \
    notesmanager.h \
    notewidget.h

FORMS += \
    mainwindow.ui \
    noteslistwidget.ui

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

// main.cpp
///////////

#include "mainwindow.h"
#include "notesmanager.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps, true);
    QApplication::setAttribute(Qt::AA_EnableHighDpiScaling,true);

    QApplication a(argc, argv);
    NotesManager manager;
    MainWindow w(manager);

    w.show();
    return a.exec();
}

//mainwindow.cpp
////////////////

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include "notesmanager.h"
#include "note.h"
#include "noteslistwidget.h"

#include <QPushButton>
#include <QMessageBox>

#include <algorithm>

MainWindow::MainWindow(NotesManager &manager, QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::MainWindow)
    , notesManager(manager)
{
    ui->setupUi(this);
    makeConnections();
    init();
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_newNoteBtn_clicked()
{
    notesManager.createNewNote();
}

void MainWindow::on_removeNoteBtn_clicked()
{
    removeNote(ui->notesListWidget->currentNoteId());
}

// handle NotesManager signals
void MainWindow::onNewNoteCreated(int id)
{
    addNoteToList(notesManager.note(id));
}

void MainWindow::onNoteContentChanged(int id)
{
    ui->notesListWidget->updateCurrentNote(notesManager.note(id));
}

// handle NotesListWidget signals
void MainWindow::onSelectedNoteChanged(int id)
{
    auto *document = notesManager.noteDocument(id);
    if(document)
    {
        ui->textEdit->setDocument(document);
       // auto cursor = ui->textEdit->textCursor();
       // cursor.movePosition(QTextCursor::End);
       // ui->textEdit->setTextCursor(cursor);
    }
}

void MainWindow::onRemoveNote(int id)
{
    removeNote(id);
}

void MainWindow::addNoteToList(const Note &note)
{
    ui->notesListWidget->addNote(note);
}

void MainWindow::removeNote(int id)
{
    QString noteTitle = notesManager.note(id).title;
    auto pressedBtn = QMessageBox::information(this,"remove note?",
                                                  QString("Are you sure you want to remove %0?").arg(noteTitle),
                                                  QMessageBox::Yes|QMessageBox::No,QMessageBox::Yes);

    if(pressedBtn == QMessageBox::Yes)
    {
        if(notesManager.count() ==1)
            ui->textEdit->setDocument(nullptr);

        ui->notesListWidget->removeCurrentNote();
        notesManager.removeNote(id);
    }
}

void MainWindow::init()
{
    auto notesList = notesManager.noteCollection();
    std::sort(notesList.begin(), notesList.end(),
              [](const Note &left, const Note &right)
                {
                    return left.lastModified < right.lastModified;
                });
    for(auto &note : notesList)
      addNoteToList(note);
}

void MainWindow::makeConnections()
{
    connect(ui->newNoteBtn, &QPushButton::click, this, &MainWindow::on_newNoteBtn_clicked);
    connect(ui->removeNoteBtn, &QPushButton::click, this, &MainWindow::on_removeNoteBtn_clicked);

    connect(&notesManager, &NotesManager::newNoteCreated,this, &MainWindow::onNewNoteCreated);
    connect(&notesManager, &NotesManager::noteContendChanged, this, &MainWindow::onNoteContentChanged);

    connect(ui->notesListWidget, &NotesListWidget::selectedNoteChanged, this, &MainWindow::onSelectedNoteChanged);
}


//MainWindow.h
//////////////

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QWidget>
#include <QPushButton>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class NotesManager;
class Note;

class MainWindow : public QWidget
{
    Q_OBJECT

public:
    MainWindow(NotesManager &manageNr, QWidget *parent = nullptr);
    ~MainWindow();

private slots:
    // handle signal for ui
    void on_newNoteBtn_clicked();
    void on_removeNoteBtn_clicked();

    // handle NotesManager signals
    void onNewNoteCreated(int id);
    void onNoteContentChanged(int id);

    // handle NotesListWidget signals
    void onSelectedNoteChanged(int id);
    void onRemoveNote(int id);

private:
    void addNoteToList(const Note &note);
    void removeNote(int id);

    void init();
    void makeConnections();
    Ui::MainWindow *ui;
    NotesManager &notesManager;
};
#endif // MAINWINDOW_H

//mainwindow.ui
///////////////

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QWidget" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>800</width>
    <height>600</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <layout class="QVBoxLayout" name="verticalLayout" stretch="0,1">
   <item>
    <layout class="QHBoxLayout" name="horizontalLayout">
     <item>
      <widget class="QPushButton" name="newNoteBtn">
       <property name="text">
        <string>New</string>
       </property>
      </widget>
     </item>
     <item>
      <widget class="QPushButton" name="removeNoteBtn">
       <property name="text">
        <string>Delete</string>
       </property>
      </widget>
     </item>
     <item>
      <spacer name="horizontalSpacer">
       <property name="orientation">
        <enum>Qt::Horizontal</enum>
       </property>
       <property name="sizeHint" stdset="0">
        <size>
         <width>40</width>
         <height>20</height>
        </size>
       </property>
      </spacer>
     </item>
    </layout>
   </item>
   <item>
    <widget class="QSplitter" name="splitter">
     <property name="orientation">
      <enum>Qt::Horizontal</enum>
     </property>
     <property name="childrenCollapsible">
      <bool>false</bool>
     </property>
     <widget class="NotesListWidget" name="notesListWidget" native="true"/>
     <widget class="QTextEdit" name="textEdit"/>
    </widget>
   </item>
  </layout>
 </widget>
 <customwidgets>
  <customwidget>
   <class>NotesListWidget</class>
   <extends>QWidget</extends>
   <header>noteslistwidget.h</header>
   <container>1</container>
  </customwidget>
 </customwidgets>
 <resources/>
 <connections/>
</ui>

//note.h
////////

#pragma once

#include <QString>
#include <QDateTime>

struct Note
{
    int id;
    QString title;
    QString content;
    QDateTime lastModified;

};

//noteslistwidget.cpp
///////////////////

#include "noteslistwidget.h"
#include "ui_noteslistwidget.h"

#include "note.h"

NotesListWidget::NotesListWidget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::NotesListWidget)
{
    ui->setupUi(this);
    connect(ui->noteList, &QListWidget::itemSelectionChanged,
            this, &NotesListWidget::onItemSlectionChanged);
}

NotesListWidget::~NotesListWidget()
{
    delete ui;
}
void NotesListWidget::addNote(const Note &note) 
{
    auto *item = new QListWidgetItem();
    ui->noteList->insertItem(0, item);

    setupNoteItem(note, item);


}
void NotesListWidget::removeCurrentNote() 
{
    auto *currentItem = ui->noteList->currentItem();
    if(currentItem != nullptr)
    {
        delete currentItem;
    }
}
void NotesListWidget::updateCurrentNote(const Note &note) 
{
    if(ui->noteList->currentRow() !=0 )
    {
        moveCurrenItemToTop(note);
    }
}

int NotesListWidget::currentNoteId()  
{
    auto *currentItem = ui->noteList->currentItem();
    int noteId =currentItem->data(Qt::UserRole).toInt();
    return noteId;
}

void NotesListWidget::onItemSlectionChanged() 
{
    auto *currentItem = ui->noteList->currentItem();
    if(currentItem)
    {
        int id = currentNoteId();
        emit selectedNoteChanged(id);
    }
}
void NotesListWidget::moveCurrenItemToTop(const Note &note) 
{
    blockSignals(true);
    auto *item = ui->noteList->takeItem(ui->noteList->currentRow());

    ui->noteList->insertItem(0,item);
    setupNoteItem(note, item);
    blockSignals(false);
}
void NotesListWidget::setupNoteItem(const Note &note, QListWidgetItem *item) 
{
    item->setText(note.title);
    item->setData(Qt::UserRole, note.id);
    ui->noteList->setCurrentItem(item);
}

// notesListWidget.h
////////////////////

#pragma once

#include <QWidget>

namespace Ui {
class NotesListWidget;
}

struct Note;
class QListWidgetItem;

class NotesListWidget : public QWidget
{
    Q_OBJECT

public:
    explicit NotesListWidget(QWidget *parent = nullptr);
    ~NotesListWidget();

    void addNote(const Note &note);
    void removeCurrentNote();
    void updateCurrentNote(const Note &note);

    int currentNoteId();

signals:
    void selectedNoteChanged(int id);

private:
    void onItemSlectionChanged();

    void moveCurrenItemToTop(const Note &note);
    void setupNoteItem(const Note &note, QListWidgetItem *item);


private:
    Ui::NotesListWidget *ui;
};

//noteslistwidget.ui
////////////////////

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>NotesListWidget</class>
 <widget class="QWidget" name="NotesListWidget">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>261</width>
    <height>579</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Form</string>
  </property>
  <layout class="QVBoxLayout" name="verticalLayout">
   <item>
    <widget class="QListWidget" name="noteList"/>
   </item>
  </layout>
 </widget>
 <resources/>
 <connections/>
</ui>

//notesmanager.cpp
//////////////////

#include "notesmanager.h"
#include "note.h"

#include <QTextDocument>
#include <QSignalMapper>

int nextNoteId();

NotesManager::NotesManager(QObject *parent) : QObject(parent)
{
    mapChangedSignalToNoteId = new QSignalMapper(this);
    connect(mapChangedSignalToNoteId, &QSignalMapper::mappedInt,
            this, &NotesManager::onNoteContentChanged);
         
    readNotes();  
    
    if(notes.size() ==0)
        createNewNote();
}

NotesManager::~NotesManager()
{
   writeNotes(); 
}

void NotesManager::createNewNote()
{
   int id = nextNoteId(); 
   auto &[note, textDocument] = notes[id];
   note.id = id;
   note.title = "new Note";
   note.lastModified = QDateTime::currentDateTime();
   textDocument = createNewTextDocument(note);
   
   emit newNoteCreated(id);
   
}

void NotesManager::removeNote(int id)
{
    notes.erase(id);
    
    if(notes.empty())
        createNewNote();
}

void NotesManager::renameNote(int id, const QString &newTitle)
{
    // todo
    //   Q_UNUSED(id);
    //   Q_UNUSED(newTitle);

       auto found = notes.find(id);
       if(found !=notes.end())
       {
           auto &[note, textDocument] = found->second;
           note.title = newTitle;
           note.lastModified = QDateTime::currentDateTime();
       }
}

const Note &NotesManager::note(int id) const
{
    return notes.at(id).first;
}

QTextDocument *NotesManager::noteDocument(int id) const
{
    auto found = notes.find(id);
    if(found != notes.end())
    {
        return found->second.second.get();
    }
    return nullptr;
}

std::vector<std::reference_wrapper<Note>>NotesManager::noteCollection()
{
    std::vector<std::reference_wrapper<Note>> out;
    for(auto &i : notes)
    {
        auto &[note, QTextDocument] =i.second;
                note.content = QTextDocument.toPlainText();
                out.push_back(note);
    }
                return out;
}
                
size_t NotesManager::count() const
{
    return notes.size();       
}

void NotesManager::onNoteContentChanged(int id)
{
    notes.at(id).first.lastModified =QDateTime::currentDateTime();    
    emit noteContendChanged(id);    
}
          
void NotesManager::readNotes()
{
      // todo              
}

void NotesManager::writeNotes()
{
      // todo
}
std::unique_ptr<QTextDocument> NotesManager::createNewTextDocument(const Note &note)
{
    auto textDocument =std::make_unique<QTextDocument>(note.content);
    connect(textDocument.get(), &QTextDocument::contentsChange,
            mapChangedSignalToNoteId, qOverload<>(&QSignalMapper::map));
    mapChangedSignalToNoteId->setMapping(textDocument.get(),note.id);

    return textDocument;
}
int nextNoteId()
{
    static int id = 0;
    return ++id;
}

//notesmanager.h
////////////////

#pragma once
#include <QObject>

#include <unordered_map>
#include <vector>
#include <utility>
#include <memory>

struct Note;

class QTextDocument;
class QSignalMapper;

class NotesManager : public QObject

{
    Q_OBJECT
public:
    explicit NotesManager(QObject *parent = nullptr);readable version of code

    ~NotesManager();
    
    void createNewNote();
    void removeNote(int id);
    void renameNote(int id, const QString &newTitle);

    const Note &note(int id) const;
    QTextDocument *noteDocument(int id) const;
    std::vector<std::reference_wrapper<Note>> noteCollection();
    size_t count() const;

signals:
    void newNoteCreated(int id);
    void noteContendChanged(int id);

private:
    void onNoteContentChanged(int id);
    void readNotes();
    void writeNotes();
    std::unique_ptr<QTextDocument> createNewTextDocument(const Note &note);

private:
    std::unordered_map<int, std::pair<Note, std::unique_ptr<QTextDocument>>> notes;
    QSignalMapper *mapChangedSignalToNoteId =nullptr;
};              

//////////////////////
// end notes.cpp

[jsulm]

@sowas said in Using more standard library function:

According to Creator Info (4.13.2) : Qt 5.15.1 (GCC 5.3.1 20160406 (Red Hat 5.3.1-6),64 bit

This is Qt version which was used to build QtCreator and doesn't matter here.
What you are using is 5.12.9

Under "3. Compiler" you should also have GCC/G++, do you? Which version is that compiler?

[sowas]

@jsulm
attached a screenshot of my monitor

[J.Hilk]

@sowas
ok, Qt 5.12 should support c++17

to exclude the compiler check what this program outputs:

#include <iostream>

int main (int argc, char *argv[])
{

    std::cout << "C++ Version: " << __cplusplus << std::endl;
}

it should be C++ Version: 201703 or higher, to support c++17

[sowas]

@J.Hilk
regrettable the result is : C++ Version: 201103.
What can I do now?

[sierdzio]

@jsulm said in Using more standard library function:

5.12.9

I think back then the config flag used to be CONFIG += c++1z.

[jsulm]

@sierdzio I guess you mean @sowas ? :-)

[J.Hilk]

Well, historically speaking, compiler vendors did not update/maintain
that part of the c++ standard very well, so I would suggest you do what @sierdzio suggested, maybe the compiler is c++17 capable after all 🤷‍♂️

After that, update your compiler, you're on linux IIRC, a platform I personally do not use, but it should be rather easy via a package manager of your trusting

[sierdzio]

@jsulm said in Using more standard library function:

@sierdzio I guess you mean @sowas ? :-)

Yes, sorry. I clicked "quote" on the first post I saw with concrete Qt version.