Re: Converting Bitmap into 2D-Array

Ulrich Eckhardt <>
Thu, 21 Feb 2008 16:43:56 +0100
Lucress Carol wrote:

But my problem is that the vector of gray values should be given to
the function which has to calculate the fft and I have never worked
before with vector.

std::vector is a class that contains a dynamically resizable array. You can
pass it to and from a function like any other type. Keep in the back of you
head that this isn't necessarily performant though, but for the beginning
this should work correctly.

I'm not an c++-expert but i guess i have to write the following
#include<vector> right?

Yes, correct. However, the question is wrong. The reason is that this is
explained in really every C++ book so you shouldn't have to ask here. If
you don't have a book, check out the book reviews at and
pick one of the better books.

Another question.what does the following statement means?I didn't know
one can implement two strutures once at the time.......

 struct bitmap {
   struct column {
     pixel const& operator[](size_t row) const;
     pixel& operator[](size_t row);

   column const& operator[](size_t col) const;
   column& operator[](size_t col);
Do you mind explaining me this?

This is called a nested type. You can nest any type and namespaces within a
namespace (including the global namespace) and you can nest types within
classes and structures (I'm not sure if you can do so with unions, too).
This is just a very convenient and clear way to group closely related

  bitmap b;
  bitmap::column const& c = b[42];
  bitmap::pixel const& p = c[13];

Note: I assumed that the type for the pixel is also nested inside class
bitmap, possibly with a simple 'typedef unsigned pixel;' or a small wrapper
class that allows you to set greyscale values.


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