Simple Function Pointer Example

[kendavistoo]

I have written a simple function pointer example which uses typedef. Hopefully it is useful for some of you all. If there are any errors or stupid mistakes, please comment on them.

main.cpp:

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.resize(300, 200);
    w.show();

    return a.exec();
}

SimpleFunctionPointer.pro:

#-------------------------------------------------
#
# Project created by QtCreator 2018-12-24T09:43:01
#
#-------------------------------------------------

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = SimpleFunctionPointer
TEMPLATE = app

# The following define makes your compiler emit warnings if you use
# any feature of Qt which has been marked as deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

CONFIG += c++11

SOURCES += \
        main.cpp \
        mainwindow.cpp

HEADERS += \
        mainwindow.h

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

mainwindow.cpp:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QDebug>
#include <QRadioButton>
#include <QButtonGroup>
#include <QPainter>
#include <QPaintEvent>
#include <QWidget>

static const int ORDER_NONE     = 0;
static const int ORDER_ASCEND   = 1;
static const int ORDER_DESCEND  = 2;

//----------

typedef bool (*ValidateFcn)(int&, int&);

//---------- class MainWindow ----------

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();

    static bool    ascending(int&, int&);
    static bool    descending(int&, int&);

    void    drawArray();

    int array[9] = { 3, 7, 9, 5, 6, 1, 8, 2, 4 };
    int arraySize = 9;

    QRadioButton*   ascendButt;
    QRadioButton*   descendButt;

    QButtonGroup*   buttGroup;

    ValidateFcn valFcn;

    int order = ORDER_NONE;

    bool doSort = false;

    bool doBubble(ValidateFcn);

protected:
    void paintEvent(QPaintEvent*);

public slots:
    void SLOT_AscendClick();
    void SLOT_DescendClick();
};

#endif // MAINWINDOW_H

mainwindow.cpp:

#include "mainwindow.h"

//---------- CONSTRUCTOR   MainWindow ----------

MainWindow :: MainWindow(QWidget *parent) : QMainWindow(parent)
{
    ascendButt  = new QRadioButton("Ascend", this);
    descendButt = new QRadioButton("Descend", this);

    ascendButt->setGeometry (40, 50, 130, 24);
    descendButt->setGeometry(40, 90, 130, 24);

    buttGroup   = new QButtonGroup(this);
    buttGroup->addButton(ascendButt, 1);
    buttGroup->addButton(descendButt, 2);
    buttGroup->setExclusive(true);

    connect(ascendButt, &QAbstractButton::toggled, this, &MainWindow::SLOT_AscendClick);
    connect(descendButt, &QAbstractButton::toggled, this, &MainWindow::SLOT_DescendClick);
}

//---------- DESTRUCTOR   ~MainWindow ----------

MainWindow :: ~MainWindow()
{

}

//---------- paintEvent ----------

void MainWindow :: paintEvent(QPaintEvent* event){

    QPainter* painter = new QPainter(this);

    //paint indicator
    int x = 10 + (int)(20 + (rand() % 10));
    int y = (this->height() - 30);
    QRect myRect(x,y,8,8);
    painter->fillRect(myRect, Qt::red);

    //----------

    if (doSort){

        doSort = false;

        switch(order){

        case ORDER_ASCEND:
            valFcn = ascending;

            if (doBubble(valFcn)){
                doSort = true;
            }//if
            break;

        case ORDER_DESCEND:
            valFcn = descending;

            if (doBubble(valFcn)){
                doSort = true;
            }//if
        }//switch

        if ( ! doSort){
            drawArray();
        }//if
    }//if doSort

    delete painter;

    update();
}

//---------- ascending ----------

bool MainWindow :: ascending(int& a, int& b){
    return b < a;
}

//---------- descending ----------

bool MainWindow :: descending(int& a, int& b){
    return b > a;
}

//---------- doBubble ----------

bool MainWindow :: doBubble(ValidateFcn vFcn){

    bool didSwap = false;

    for (int i=0; i<(arraySize -1); i++){

        int a = array[i];
        int b = array[i+1];
        if ( (*vFcn)(a, b) ){
            int cpy = array[i];
            array[i] = array[i+1];
            array[i+1] = cpy;
            didSwap = true;
        }//if
    }//for i

    return didSwap;
}

//---------- drawArray ----------

void MainWindow :: drawArray(){

    QString str;
    for (int i=0; i<9; i++){
        str.append(QString::number(array[i]));
        str.append(" ");
    }
    qDebug()<<str;
}

//---------- SLOT_AscendClick ----------

void MainWindow :: SLOT_AscendClick(){

    if (ascendButt->isChecked()){
        order = ORDER_ASCEND;
        doSort = true;
        qDebug()<<"\nORDER_ASCEND";
        drawArray();
    }//if
}

//---------- SLOT_DescendClick ----------

void MainWindow :: SLOT_DescendClick(){

    if (descendButt->isChecked()){
        order = ORDER_DESCEND;
        doSort = true;
        qDebug()<<"\nORDER_DESCEND";
        drawArray();
    }//if
}

[SGaist]

Hi,

At least one thing: don't do the sorting un your paintEvent, it just consumes processing power at the wrong time. Do the sorting when you change its type and once done trigger the update to your UI.