Programming Forums > Application Development > C++

brad sue · Nov 1st, 2006, 9:38 AM

I made the changes, and I also change the overload operator and draw so that it display correctly in the monitor.

I succeded to have to correct form ( the 20X30 table) but again a run time error:
Ichange the 2 entity like this:

(Toggle Plain Text)

   void Screen::draw()const
   {
        for( int i=0;i<height;i++)
            {for( int j=0;j<width;j++)
                 cout<<*(pixels+(i*width)+j);
                 cout<<endl;}
                 
   } 
        
    ostream& operator<<(ostream & out, const Screen & TV)
    { 
             for(int i=0;i<TV.height;i++)
                 {for(int j=0;j<TV.width;j++)
                    out<<*(TV.pixels+(i*TV.width)+j);
                    out<<endl;}// i changed the position of  the'}' here and in draw().
    }

debugging run time error is new I found them difficult to catch. what is the deal with those?
B.

The Dark · Nov 1st, 2006, 11:12 AM

When I run it, I only get the run time error when a rectangle tries to write outside the screen. Then I get a runtime when it tries to free the screen.

Can you show your changed code?

brad sue · Nov 1st, 2006, 3:42 PM

I did disable all commands of other functions.
Here is my Screen class:

(Toggle Plain Text)

  class Screen
   {
         private:
                 char* pixels;
                 int height;//rows
                 int width;//columns
         public: 
                friend ostream& operator<<(ostream & out, const Screen & TV);
                Screen(int=10, int=10);
                Screen(const Screen&);
                ~Screen(void);
                void setH(int );
                int getH(void)const;
                void setW(int);
                int getW() const;
                void setPoint(const Point&,char);
                void resetPoint(const Point&);
                void clear(void);
                void draw(void)const;
   };

// implementation of screen class

   Screen::Screen(int r,int c)
   {
         int size;
         height=r;
         width=c;
         size=r*c;
         pixels=new char[size];
         for(int i=0;i<r;i++)
            {
              for(int j=0;j<c;j++)
                 {
                  *(pixels+(i*c)+j)='.';
                  }
            }
   }             
      
      
   Screen::~Screen(){delete []pixels;}
   
   void Screen::setPoint(const Point & object, char c)
   {
        int i=object.getX();
        int j=object.getY();        
        *(pixels+(i*width)+j)=c;
   }          
                 
      
   
   void Screen::resetPoint(const Point& object)
   {
        int x_del,y_del;
        x_del=object.getX();
        y_del=object.getY();
        *(pixels+(x_del*width)+y_del)='.';
   }   
   
   void Screen::clear()
   { int i,j;
         for(i=0;i<height;i++){
             for(j=0;j<width;j++)
                 *(pixels+(i*width)+j)='.';}
   }
    
    void Screen::setH(int row)
    {
         height=row;
    }
    
    int Screen::getH()const{ return height;}
    
    void Screen::setW(int col)
    {
         width=col;
    }
    
    int Screen::getW() const{ return width;}
    
         
    void Screen::draw()const
   {
        for( int i=0;i<height;i++)
            for( int j=0;j<width;j++)
                { cout<<*(pixels+(i*width)+j);
                 cout<<endl;}
                 
   } 
        
    ostream& operator<<(ostream & out, const Screen & TV)
    { 
             for(int i=0;i<TV.height;i++)
                 {for(int j=0;j<TV.width;j++)
                    out<<*(TV.pixels+(i*TV.width)+j);
                    out<<endl;}
    }
  

for the moment my main is:
int main()
{
    Screen ecran(20,30);
    cout<<"\n\nPrinting a blank Screen"<<endl;
    cout<<ecran<<endl;
    return 0;
}

  class Screen
   {
         private:
                 char* pixels;
                 int height;//rows
                 int width;//columns
         public: 
                friend ostream& operator<<(ostream & out, const Screen & TV);
                Screen(int=10, int=10);
                Screen(const Screen&);
                ~Screen(void);
                void setH(int );
                int getH(void)const;
                void setW(int);
                int getW() const;
                void setPoint(const Point&,char);
                void resetPoint(const Point&);
                void clear(void);
                void draw(void)const;
   };

// implementation of screen class

   Screen::Screen(int r,int c)
   {
         int size;
         height=r;
         width=c;
         size=r*c;
         pixels=new char[size];
         for(int i=0;i<r;i++)
            {
              for(int j=0;j<c;j++)
                 {
                  *(pixels+(i*c)+j)='.';
                  }
            }
   }             
      
      
   Screen::~Screen(){delete []pixels;}
   
   void Screen::setPoint(const Point & object, char c)
   {
        int i=object.getX();
        int j=object.getY();        
        *(pixels+(i*width)+j)=c;
   }          
                 
      
   
   void Screen::resetPoint(const Point& object)
   {
        int x_del,y_del;
        x_del=object.getX();
        y_del=object.getY();
        *(pixels+(x_del*width)+y_del)='.';
   }   
   
   void Screen::clear()
   { int i,j;
         for(i=0;i<height;i++){
             for(j=0;j<width;j++)
                 *(pixels+(i*width)+j)='.';}
   }
    
    void Screen::setH(int row)
    {
         height=row;
    }
    
    int Screen::getH()const{ return height;}
    
    void Screen::setW(int col)
    {
         width=col;
    }
    
    int Screen::getW() const{ return width;}
    
         
    void Screen::draw()const
   {
        for( int i=0;i<height;i++)
            for( int j=0;j<width;j++)
                { cout<<*(pixels+(i*width)+j);
                 cout<<endl;}
                 
   } 
        
    ostream& operator<<(ostream & out, const Screen & TV)
    { 
             for(int i=0;i<TV.height;i++)
                 {for(int j=0;j<TV.width;j++)
                    out<<*(TV.pixels+(i*TV.width)+j);
                    out<<endl;}
    }
  

for the moment my main is:
int main()
{
    Screen ecran(20,30);
    cout<<"\n\nPrinting a blank Screen"<<endl;
    cout<<ecran<<endl;
    return 0;
}

It is the only changes I made beside the the two I did show above.

The Dark · Nov 1st, 2006, 5:58 PM

I don't know if it causes the problem, but you are not returning the stream in your << function.
The compiler should have warned you about this problem.

brad sue · Nov 2nd, 2006, 1:31 AM

thank you !Yes that was the issue .
I am struggling with a function that reduces the size of the screen by a factor x.
The problem is that I dont succeed to keep the location of the painted point s on the screen canvas. the redcution is done by deleting the remaining points
I coded this::

(Toggle Plain Text)

    void Screen::shrink(int reduc)
    { 
         if((reduc<height)&&(reduc<width))
           {  height=height/reduc;
              width=width/reduc;
                  for( int i=height;i<0;i--)
                      for( int j=width;j<0;j--)
                        delete[](pixels+(i*width)+i);
           }//end if           
    }

if the screen is:
4455*888
4455*888
5555*888
*******

if we do shrink(2), the screen should be:
4455
4455

In my function the size it OK but the location of the points is not kept. because I don't know how to 'jump' one line up to start deleting again.
I continue to work on it but Please if someone has a suggestion please send it to me.
B.

The Dark · Nov 2nd, 2006, 6:36 AM

Since you allocted pixels as one block of char, it is a very bad idea to try to delete[] the chars individually. You either can leave the block at its original size (and have some unused memory) or allocate a new block, copy the contents you want across and then delete the old block.

As for copying the data across to the new size, you need to keep track of the old size and use that to find the location of the pixels you want to copy from the old data.

DaWei · Nov 2nd, 2006, 7:12 AM

Just an additional caveat, though it's implicit in The Dark's post: don't forget that your destructor is going to delete 'pixels', so be wary of how you mess with that.

brad sue · Nov 2nd, 2006, 8:03 AM

I think it would be better to change my constructor and destructor as allocate memory individually. I will try to do this first then tackle the 'shrink' again.
thank you for the suggestions.

brad sue · Nov 2nd, 2006, 2:51 PM

I tried to change my constructor but it fails.Then I tried this

(Toggle Plain Text)

void Screen::shrink(int reduc)
    { 
         if((reduc<height)&&(reduc<width))
           {  
            int newrow,newcol;
            newrow=height/reduc;
            newcol=width/reduc;
            char *newpixels=new char[newrow*newcol];
                //iterate the old block line by line            
            for ( int i = 0; i < newrow; i++)
              {
               memcpy( newpixels + (i*newcol), pixels + (i*width), newcol);  //copy only the required amount of data
              }
               //delete the old data     
            delete []pixels;      
            pixels = newpixels;
            
             } 
   }

I dont see my mistake but it does not work. My problem is that I still fail to keep track of the old data and save them in newpixels.
See where I am wrong in my code?

The Dark · Nov 2nd, 2006, 3:32 PM

Same problem as in post #29, which was answered in post #30

Nov 1st, 2006, 9:38 AM	#31
brad sue Hobbyist Programmer Join Date: Mar 2006 Posts: 115 Rep Power: 3	I made the changes, and I also change the overload operator and draw so that it display correctly in the monitor. I succeded to have to correct form ( the 20X30 table) but again a run time error: Ichange the 2 entity like this: (Toggle Plain Text) void Screen::draw()const { for( int i=0;i<height;i++) {for( int j=0;j<width;j++) cout<<(pixels+(iwidth)+j); cout<<endl;} } ostream& operator<<(ostream & out, const Screen & TV) { for(int i=0;i<TV.height;i++) {for(int j=0;j<TV.width;j++) out<<(TV.pixels+(iTV.width)+j); out<<endl;}// i changed the position of the'}' here and in draw(). } void Screen::draw()const { for( int i=0;i<height;i++) {for( int j=0;j<width;j++) cout<<(pixels+(iwidth)+j); cout<<endl;} } ostream& operator<<(ostream & out, const Screen & TV) { for(int i=0;i<TV.height;i++) {for(int j=0;j<TV.width;j++) out<<(TV.pixels+(iTV.width)+j); out<<endl;}// i changed the position of the'}' here and in draw(). } debugging run time error is new I found them difficult to catch. what is the deal with those? B. Last edited by brad sue; Nov 1st, 2006 at 10:12 AM.

Nov 2nd, 2006, 1:31 AM	#35
brad sue Hobbyist Programmer Join Date: Mar 2006 Posts: 115 Rep Power: 3	thank you !Yes that was the issue . I am struggling with a function that reduces the size of the screen by a factor x. The problem is that I dont succeed to keep the location of the painted point s on the screen canvas. the redcution is done by deleting the remaining points I coded this:: (Toggle Plain Text) void Screen::shrink(int reduc) { if((reduc<height)&&(reduc<width)) { height=height/reduc; width=width/reduc; for( int i=height;i<0;i--) for( int j=width;j<0;j--) delete[](pixels+(iwidth)+i); }//end if } void Screen::shrink(int reduc) { if((reduc<height)&&(reduc<width)) { height=height/reduc; width=width/reduc; for( int i=height;i<0;i--) for( int j=width;j<0;j--) delete[](pixels+(iwidth)+i); }//end if } if the screen is: 4455888 4455888 5555888 ****** if we do shrink(2), the screen should be: 4455 4455 In my function the size it OK but the location of the points is not kept. because I don't know how to 'jump' one line up to start deleting again. I continue to work on it but Please if someone has a suggestion please send it to me. B.

Nov 2nd, 2006, 7:12 AM	#37
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Just an additional caveat, though it's implicit in The Dark's post: don't forget that your destructor is going to delete 'pixels', so be wary of how you mess with that. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Nov 2nd, 2006, 2:51 PM	#39
brad sue Hobbyist Programmer Join Date: Mar 2006 Posts: 115 Rep Power: 3	I tried to change my constructor but it fails.Then I tried this (Toggle Plain Text) void Screen::shrink(int reduc) { if((reduc<height)&&(reduc<width)) { int newrow,newcol; newrow=height/reduc; newcol=width/reduc; char newpixels=new char[newrownewcol]; //iterate the old block line by line for ( int i = 0; i < newrow; i++) { memcpy( newpixels + (inewcol), pixels + (iwidth), newcol); //copy only the required amount of data } //delete the old data delete []pixels; pixels = newpixels; } } void Screen::shrink(int reduc) { if((reduc<height)&&(reduc<width)) { int newrow,newcol; newrow=height/reduc; newcol=width/reduc; char newpixels=new char[newrownewcol]; //iterate the old block line by line for ( int i = 0; i < newrow; i++) { memcpy( newpixels + (inewcol), pixels + (iwidth), newcol); //copy only the required amount of data } //delete the old data delete []pixels; pixels = newpixels; } } I dont see my mistake but it does not work. My problem is that I still fail to keep track of the old data and save them in newpixels. See where I am wrong in my code?

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Nov 1st, 2006, 11:12 AM	#32
The Dark Expert Programmer Join Date: Jun 2005 Posts: 810 Rep Power: 4	When I run it, I only get the run time error when a rectangle tries to write outside the screen. Then I get a runtime when it tries to free the screen. Can you show your changed code?

Nov 1st, 2006, 3:42 PM	#33
brad sue Hobbyist Programmer Join Date: Mar 2006 Posts: 115 Rep Power: 3	I did disable all commands of other functions. Here is my Screen class: (Toggle Plain Text) class Screen { private: char* pixels; int height;//rows int width;//columns public: friend ostream& operator<<(ostream & out, const Screen & TV); Screen(int=10, int=10); Screen(const Screen&); ~Screen(void); void setH(int ); int getH(void)const; void setW(int); int getW() const; void setPoint(const Point&,char); void resetPoint(const Point&); void clear(void); void draw(void)const; }; // implementation of screen class Screen::Screen(int r,int c) { int size; height=r; width=c; size=rc; pixels=new char[size]; for(int i=0;i<r;i++) { for(int j=0;j<c;j++) { (pixels+(ic)+j)='.'; } } } Screen::~Screen(){delete []pixels;} void Screen::setPoint(const Point & object, char c) { int i=object.getX(); int j=object.getY(); (pixels+(iwidth)+j)=c; } void Screen::resetPoint(const Point& object) { int x_del,y_del; x_del=object.getX(); y_del=object.getY(); (pixels+(x_delwidth)+y_del)='.'; } void Screen::clear() { int i,j; for(i=0;i<height;i++){ for(j=0;j<width;j++) (pixels+(iwidth)+j)='.';} } void Screen::setH(int row) { height=row; } int Screen::getH()const{ return height;} void Screen::setW(int col) { width=col; } int Screen::getW() const{ return width;} void Screen::draw()const { for( int i=0;i<height;i++) for( int j=0;j<width;j++) { cout<<(pixels+(iwidth)+j); cout<<endl;} } ostream& operator<<(ostream & out, const Screen & TV) { for(int i=0;i<TV.height;i++) {for(int j=0;j<TV.width;j++) out<<(TV.pixels+(iTV.width)+j); out<<endl;} } for the moment my main is: int main() { Screen ecran(20,30); cout<<"\n\nPrinting a blank Screen"<<endl; cout<<ecran<<endl; return 0; } class Screen { private: char pixels; int height;//rows int width;//columns public: friend ostream& operator<<(ostream & out, const Screen & TV); Screen(int=10, int=10); Screen(const Screen&); ~Screen(void); void setH(int ); int getH(void)const; void setW(int); int getW() const; void setPoint(const Point&,char); void resetPoint(const Point&); void clear(void); void draw(void)const; }; // implementation of screen class Screen::Screen(int r,int c) { int size; height=r; width=c; size=rc; pixels=new char[size]; for(int i=0;i<r;i++) { for(int j=0;j<c;j++) { (pixels+(ic)+j)='.'; } } } Screen::~Screen(){delete []pixels;} void Screen::setPoint(const Point & object, char c) { int i=object.getX(); int j=object.getY(); (pixels+(iwidth)+j)=c; } void Screen::resetPoint(const Point& object) { int x_del,y_del; x_del=object.getX(); y_del=object.getY(); (pixels+(x_delwidth)+y_del)='.'; } void Screen::clear() { int i,j; for(i=0;i<height;i++){ for(j=0;j<width;j++) (pixels+(iwidth)+j)='.';} } void Screen::setH(int row) { height=row; } int Screen::getH()const{ return height;} void Screen::setW(int col) { width=col; } int Screen::getW() const{ return width;} void Screen::draw()const { for( int i=0;i<height;i++) for( int j=0;j<width;j++) { cout<<(pixels+(iwidth)+j); cout<<endl;} } ostream& operator<<(ostream & out, const Screen & TV) { for(int i=0;i<TV.height;i++) {for(int j=0;j<TV.width;j++) out<<(TV.pixels+(i*TV.width)+j); out<<endl;} } for the moment my main is: int main() { Screen ecran(20,30); cout<<"\n\nPrinting a blank Screen"<<endl; cout<<ecran<<endl; return 0; } It is the only changes I made beside the the two I did show above.

Nov 1st, 2006, 5:58 PM	#34
The Dark Expert Programmer Join Date: Jun 2005 Posts: 810 Rep Power: 4	I don't know if it causes the problem, but you are not returning the stream in your << function. The compiler should have warned you about this problem.

Nov 2nd, 2006, 6:36 AM	#36
The Dark Expert Programmer Join Date: Jun 2005 Posts: 810 Rep Power: 4	Since you allocted pixels as one block of char, it is a very bad idea to try to delete[] the chars individually. You either can leave the block at its original size (and have some unused memory) or allocate a new block, copy the contents you want across and then delete the old block. As for copying the data across to the new size, you need to keep track of the old size and use that to find the location of the pixels you want to copy from the old data.

Nov 2nd, 2006, 8:03 AM	#38
brad sue Hobbyist Programmer Join Date: Mar 2006 Posts: 115 Rep Power: 3	I think it would be better to change my constructor and destructor as allocate memory individually. I will try to do this first then tackle the 'shrink' again. thank you for the suggestions.

Nov 2nd, 2006, 3:32 PM	#40
The Dark Expert Programmer Join Date: Jun 2005 Posts: 810 Rep Power: 4	Same problem as in post #29, which was answered in post #30

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