Cannot open include file " but I can create objects "

Project try

the code " I changed the project to solve the first problem so I named the class to another name "

imp:
@
#include "checkclass.h"

checkclass::checkclass(QWidget parent):
QWidget(){
edit = new QLineEdit;
edit1=new QLineEdit;

     left= new QHBoxLayout;
     Main=new QHBoxLayout;
        edit->setMaximumWidth(20);
        edit->setFixedWidth(20);
        edit->setValidator(Valid);
        edit1->setMaximumWidth(20);
        edit1->setFixedWidth(20);
        edit1->setValidator(Valid);
        QObject:: connect(edit,SIGNAL(editingFinished()),this,SLOT(convert));
               QObject:: connect(edit1,SIGNAL(editingFinished()),this,SLOT(convert1));
        left->addWidget(edit);
        left->addWidget(edit1);
        Main->addLayout(left);

        setLayout(Main);

}

void checkclass::convert(){
QString numbertext=edit->text();
int x=numbertext.toInt();

}
void checkclass::convert1(){
QString numbertext=edit1->text();
int y=numbertext.toInt();

}

@

header:
@
#ifndef CHECKCLASS_H
#define CHECKCLASS_H
#include<QLabel>
#include<QHBoxLayout>
#include<QLineEdit>
#include<QIntValidator>
#include<QWidget>
class checkclass : public QWidget
{
public:
checkclass(QWidget parent);

void convert();
    void convert1();
private:
    QLineEdit *edit;
    QLineEdit *edit1;
QIntValidator *Valid;
    QHBoxLayout *left;

    QHBoxLayout *Main;

};

#endif // CHECKCLASS_H
@

SGaist

Valid is not initialized

Project try

same problem :(

Project try

@SGaist , Hopefully you didn't go to sleep yet , I really need your help , because tomorrow I want to focus on studying for my mid term exam :D

Project try

The problem happens only when I use show function like for example:

myclass *A;
A->show();

it crashes , when I don't use show() my program runs just fine in the backround.

JKSH

[quote author="Project try" date="1394235877"]The problem happens only when I use show function like for example:

myclass *A;
A->show();

it crashes , when I don't use show() my program runs just fine in the backround.[/quote]Like SGaist said, you didn't initialize your pointer. A does not point to a valid object yet, so it will cause problems if you try to use it. It's not just show(), ANY function can cause a crash -- it might not crash immediately, but will crash some time later.

Call new to initialize your pointer. This is a very fundamental (and very important) concept of C++ by the way; if you are not familiar with it, I highly recommend reading a tutorial about pointers.

Project try

Thanks man ^^ , it worked

but can you please tell me why did we put : QWidget *parent in the arguments of the constructor ? even though we didn't send any argument but it was a default so what's the point ?

and since it didn't take any argument there's no need to delete that parent pointer ? , because I saw a lot of examples and most of them use it like I said but they didn't really explain why.

Project try

Good night , I need to sleep , thanks guys for helping me , and sorry for asking lots of question :(

SGaist

So that you can reuse your widget the same way you would a standard Qt widget.

Even if you don't reuse it somewhere else, it's good practice to keep a consistent code base. You never know who will use your code later

JKSH

Parent-child relationships have multiple uses in Qt. One of them is memory management. When a parent object is deleted, it will automatically delete its child objects. Thus, you should never store or delete the parent pointer.

[quote]
@
checkclass::checkclass(QWidget parent):
QWidget(){
...
@
[/quote]You have not made use of the parent pointer. Pass it to the QWidget constructor, and let Qt take care of things in the background:

@
checkclass::checkclass(QWidget parent):
QWidget(parent){
...
@