Minesweeper. segfault at recursiv check - c++

Question

i am trying to programm Minesweeper with Qt in c++11.
If i press a button with 0 bombs, i want to check for buttons around this button and if they have 0 bombs, too. If they have 0 bombs, i want to check the buttons. (picture: red square)
This is my button-class:
#ifndef ABUTTON_H
#define ABUTTON_H
#include "QPushButton"
#include "QMouseEvent"
class AButton : public QPushButton
{
Q_OBJECT
public:
AButton(QWidget* parent);
//AButton();
~AButton();
bool& set(bool state); //set bomb state
bool get(); //get bomb state
void increment_counter(); //increment counter for surrounding bombs
int get_counter(); //get bomb counter
bool get_locked(); //is it locked (->flagged)
void set_locked(bool); //set it to locked
AButton* get_Button(char c); //get Button above, beneath, left, right
void set_Button(AButton* Button, char c); //set Button above, ...; char is for setting the right one
private:
bool bomb; //is button a bomb
int Nachbar_Bomben; // how many bombs around this button
bool locked; // is the button locked
AButton* b_links; //pointer to the button to the left
AButton* b_rechts; //pointer to the button to the right
AButton* b_oben; //pointer to the button above
AButton* b_unten; //pointer to the button beneath
public slots:
void mousePressEvent(QMouseEvent *event);
signals:
void rightclicked();
void leftclicked();
};
#endif // ABUTTON_H
This is what happens if a button is clicked:
void Layout::ButtonClicked()
{
char Buffer [50];
AButton *clickedButton = qobject_cast <AButton*>(sender()); //which button
if (!clickedButton->get_locked())
{
clickedButton->setChecked(1); //set button to checked
{
if (clickedButton->get()) //Is button a bomb?
{
clickedButton->setText(QString ("B"));
Fehlermeldung *Fehler = new Fehlermeldung(); //make error window
Fehler->show();
}
else
{
if(clickedButton->get_counter() == 0) //has this button 0 bombs?
{
check_for_surrounding_bombs(clickedButton); //start the recursiv check, if there are buttons with 0 bombs around
}
else
{
sprintf(Buffer, "%i", clickedButton->get_counter());
clickedButton->setText(QString (Buffer)); //write how many bombs are in this button
}}}}}
My problem is, that i get a SegFault by calling the function "check_for_surrounding_bombs".
void Layout::check_for_surrounding_bombs(AButton* clickedButton) //function doesnt work
{
if (clickedButton->get_Button('o')) //does the button above exist?
{
if (clickedButton->get_Button('o')->get_counter()== 0) //has this button 0 bombs
{
clickedButton->get_Button('o')->setText(QString ("")); // write nothing in it
if (!clickedButton->get_Button('o')->get_locked()) //if it isnt locked (= set flag)
{
clickedButton->get_Button('o')->setChecked(1); //set the button to checked
}
check_for_surrounding_bombs(clickedButton->get_Button('o')); //do the same thing for the button above
}
//... the function does the same with the buttons to the left, right, beneath
I am unsure if my recursiv-approach is the right way.
The debugger gives me this error when calling the function "check_for_surrounding_bombs(clickedButton);":
enter image description here
Implementation of the get_Button member fct.
AButton* AButton::get_Button(char c)
{
if (c == 'o')
return b_oben; //return button above
else if (c == 'u')
return b_unten; //return button beneath
else if (c == 'l')
return b_links; //return button to the left
else if (c == 'r')
return b_rechts; //return button to the right
else
return 0;
}
Any idea?
Thank you in advance.

Answer 1

The crash is probably caused by a stack overflow. This occurs because your recursive solution has no mechanism to simplify the problem.
If you change the state of each button you have visited before recursing, then the problem would become bounded and your problem mostly go away.
A recursive solution requires some stack for each step in the solution. This is a relatively limited resource, as the stack has a bound, and can't grow into memory used for another purpose. So this case, if you had a grid layout with 100x100 elements, you could have 10,000 steps.
As such I would look to another non-recursive solution, where you create a vector or list of items left to visit, and add items to that.
It is still imperative
Don't add a location twice to the list.
Don't visit a location again, after it has been visited.