Why does a vector fail here?
JoeC
to hold my bitmap data but when I use this algorithm it fails:
for(index = 0; index < dwn; index++){
memcpy(&temp[((dwn-1) - index)*acc],
&bitData[index*acc],acc);}
The vector is declared in the header and in the constuctor I fill it
with zeros as a default.
Size is = acc*dwn;
Default 16*16 bitmap;
for(int lp = 0; lp != size; lp++){
bitData.push_back(0);
}
If I add this the program does not crash:
BYTE* bitmap::flip(){
int acc = bmi.bmiHeader.biWidth;
int dwn = bmi.bmiHeader.biHeight;
int index;
BYTE *temp2 = new BYTE[bitData.size()];
for(int l=0; l < bitData.size();l++){
temp2[l]=bitData[l];
}
BYTE * temp = new BYTE[acc*dwn];
for(index = 0; index < dwn; index++){
memcpy(&temp[((dwn-1) - index)*acc],
&temp2[index*acc],acc);}
return temp;
}
I have written a bitmap before and used a vector to hold the graphics
data but this object trying to do a DIB bitmap is giving me all kinds
of problems. The algorithm works in a function but when I try to put
the same information in an object it fails. Anything else I can add
to help explain the problem. I often have problems asking questions
on more complex problems because it can be cumbersome to post from
several files both .h and .cpp.
Öö Tiib
> I am writing a program to display bitmaps and I want to use a vector
> to hold my bitmap data but when I use this algorithm it fails:
>
> for(index = 0; index < dwn; index++){
> memcpy(&temp[((dwn-1) - index)*acc],
> &bitData[index*acc],acc);}
Seems algorithm like any other how it fails? This sounds like simple
typo outside of what you have posted.
>
> The vector is declared in the header and in the constuctor I fill it
> with zeros as a default.
The vector named 'temp'? Usually people do not declare such vectors in
header files.
> Size is = acc*dwn;
> Default 16*16 bitmap;
This can not compile. You have to describe a context where it
compiles.
> for(int lp = 0; lp != size; lp++){
> bitData.push_back(0);
> }
Usually this is done in constructor like:
std::vector<BYTE> bitData(size, 0);
> If I add this the program does not crash:
>
> BYTE* bitmap::flip(){
>
> int acc = bmi.bmiHeader.biWidth;
> int dwn = bmi.bmiHeader.biHeight;
> int index;
>
> BYTE *temp2 = new BYTE[bitData.size()];
> for(int l=0; l < bitData.size();l++){
> temp2[l]=bitData[l];
> }
>
> BYTE * temp = new BYTE[acc*dwn];
>
> for(index = 0; index < dwn; index++){
> memcpy(&temp[((dwn-1) - index)*acc],
> &temp2[index*acc],acc);}
>
> return temp;
> }
Yes. If this does not crash then all is fine with bitData vector.
Problem is with these temps of yours ... or odd variables with 3
character names.
> I have written a bitmap before and used a vector to hold the graphics
> data but this object trying to do a DIB bitmap is giving me all kinds
> of problems. The algorithm works in a function but when I try to put
> the same information in an object it fails. Anything else I can add
> to help explain the problem. I often have problems asking questions
> on more complex problems because it can be cumbersome to post from
> several files both .h and .cpp.
Do not worry. Free land and non-moderated group. Make example (as
lengthy as you made non-crashing one) with vector usage that crashes.
It is highly probable you discover your mistake in the process.
Jorgen Grahn
> I am writing a program to display bitmaps and I want to use a vector
> to hold my bitmap data but when I use this algorithm it fails:
>
> for(index = 0; index < dwn; index++){
> memcpy(&temp[((dwn-1) - index)*acc],
> &bitData[index*acc],acc);}
This is completely out of context so I have no idea what you're doing,
but memcpy() is dangerous (and almost always pointless) to use on
anything which may be an object -- for example a std::vector.
(It's also used pointlessly surprisingly often in C code -- I have
lost count of all the complicated memcpy() calls I've replaced
with straight struct assignments over the years.)
...
> Anything else I can add
> to help explain the problem. I often have problems asking questions
> on more complex problems because it can be cumbersome to post from
> several files both .h and .cpp.
http://en.wikipedia.org/wiki/Pastebin
perhaps with the core part of the problem quoted in the posting.
/Jorgen
--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .