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From: JoeC on 24 Mar 2010 20:22
I am writing an object with an array. I have an array of bits based
on a 2d grid. I declare the grid 1d array with a pointer because the
array will change size eventually. But I create the array, assign all
the elements to 0 then in an accesor function I want to change the
values of inside the array.

class bitmap{

BYTE * bits;
....

bitmap::bitmap(void){

acc=16;
dwn=16;

bits = new BYTE[acc*dwn];

for(int lp =0; lp > (acc*dwn); lp++){
bits[lp]=0;
}
....

It crashes here

void bitmap::mod(int ac, int dn, BYTE col){

bits[(acc*dn)+ac] = col; <--Crashes.

}






From: Ben Bacarisse on 24 Mar 2010 20:35
JoeC <enki034(a)yahoo.com> writes:

> I am writing an object with an array. I have an array of bits based
> on a 2d grid. I declare the grid 1d array with a pointer because the
> array will change size eventually. But I create the array, assign all
> the elements to 0 then in an accesor function I want to change the
> values of inside the array.
>
> class bitmap{
>
> BYTE * bits;
> ...
>
> bitmap::bitmap(void){
>
> acc=16;
> dwn=16;
>
> bits = new BYTE[acc*dwn];
>
> for(int lp =0; lp > (acc*dwn); lp++){

This won't do anything. You probably meant <.

> bits[lp]=0;
> }
> ...
>
> It crashes here
>
> void bitmap::mod(int ac, int dn, BYTE col){
>
> bits[(acc*dn)+ac] = col; <--Crashes.

The obvious answer is that acc*dn + ac > 255 or < 0.

> }

In fact, the problem may be somewhere else. There is not enough data
to even hazard a guess, but using a memory checking tool like valgrind
will help you find it faster. BTW, it's usually more helpful to say
what actually happens rather than just "crashes".

--
Ben.
From: JoeC on 31 Mar 2010 19:26
On Mar 24, 7:35 pm, Ben Bacarisse <ben.use...(a)bsb.me.uk> wrote:
> JoeC <enki...(a)yahoo.com> writes:
> > I am writing an object with an array.  I have an array of bits based
> > on a 2d grid.  I declare the grid 1d array with a pointer because the
> > array will change size eventually.  But I create the array, assign all
> > the elements to 0 then in an accesor function I want to change the
> > values of inside the array.
>
> > class bitmap{
>
> >   BYTE * bits;
> > ...
>
> > bitmap::bitmap(void){
>
> >    acc=16;
> >    dwn=16;
>
> >    bits = new BYTE[acc*dwn];
>
> >    for(int lp =0; lp > (acc*dwn); lp++){
>
> This won't do anything.  You probably meant <.
>
> >            bits[lp]=0;
> >      }
> > ...
>
> > It crashes here
>
> > void bitmap::mod(int ac, int dn, BYTE col){
>
> >    bits[(acc*dn)+ac] = col;   <--Crashes.
>
> The obvious answer is that acc*dn + ac > 255 or < 0.
>
> > }
>
> In fact, the problem may be somewhere else.  There is not enough data
> to even hazard a guess, but using a memory checking tool like valgrind
> will help you find it faster.  BTW, it's usually more helpful to say
> what actually happens rather than just "crashes".
>
> --
> Ben.

I am having various problems with this program. I am not sure how to
present the problem and in some cases where to look. I am trying to
do create a bitmap and there are some parts of what I am doing I don't
fully understand or where to go to get what I am looking for.

thanks.
From: JoeC on 31 Mar 2010 20:36
On Mar 31, 6:26 pm, JoeC <enki...(a)yahoo.com> wrote:
> On Mar 24, 7:35 pm, Ben Bacarisse <ben.use...(a)bsb.me.uk> wrote:
>
>
>
> > JoeC <enki...(a)yahoo.com> writes:
> > > I am writing an object with an array.  I have an array of bits based
> > > on a 2d grid.  I declare the grid 1d array with a pointer because the
> > > array will change size eventually.  But I create the array, assign all
> > > the elements to 0 then in an accesor function I want to change the
> > > values of inside the array.
>
> > > class bitmap{
>
> > >   BYTE * bits;
> > > ...
>
> > > bitmap::bitmap(void){
>
> > >    acc=16;
> > >    dwn=16;
>
> > >    bits = new BYTE[acc*dwn];
>
> > >    for(int lp =0; lp > (acc*dwn); lp++){
>
> > This won't do anything.  You probably meant <.
>
> > >            bits[lp]=0;
> > >      }
> > > ...
>
> > > It crashes here
>
> > > void bitmap::mod(int ac, int dn, BYTE col){
>
> > >    bits[(acc*dn)+ac] = col;   <--Crashes.
>
> > The obvious answer is that acc*dn + ac > 255 or < 0.
>
> > > }
>
> > In fact, the problem may be somewhere else.  There is not enough data
> > to even hazard a guess, but using a memory checking tool like valgrind
> > will help you find it faster.  BTW, it's usually more helpful to say
> > what actually happens rather than just "crashes".
>
> > --
> > Ben.
>
> I am having various problems with this program.  I am not sure how to
> present the problem and in some cases where to look.  I am trying to
> do create a bitmap and there are some parts of what I am doing I don't
> fully understand or where to go to get what I am looking for.
>
> thanks.

I have been going through my program and trying to find flaws. I am
finding some and getting it to run. Most of my problems deal with a
simple array using dynamic memory. I can do that or a vector. I do
need it to change sizes because I will make the graphic expandable
where I can put multiple icons on the same graphic. I have done this
program before now I am adding color bitmaps instead of monochrome.
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