Maybe you should be looking at std::advance? Eli Pulsifer wrote:

Hello,

I have a situation which is probably quite common and already addressed by boost.

So rather than write it my self, maybe someone can point me to the answer.

I’ve got a geometry class that needs to expose iterators for the underling vertex components.

Example:

Class Vertex

{

positions_iterator PositionsBegin();

positions_iterator PositionsEnd();

normals_iterator NormalsBegin();

normals _iterator NormalsEnd();

…

}

The first problem is depending on the format of the underling vertices, the stride between the data elements will change.

Is there some easy way to implement this?

I think writing my own using the boost::iterator_adapter is probably the way to go.

Second problem is more involved.

The texture data not only has a stride but a variable number of elements.

Some vertices have 2 texture coordinates, some 3, some even more.

Id love to define this iterator like this:

stride_iterator< pair<float_iterator, float_iterator> > tex_coord_iterator;

then create the iterator:

stride_tupel_iterator< pair<float_iterator, float_iterator> >( pFirstTexCoord, texCoordStride, texCoordCount );

then use it:

stride_tupel_iterator< pair<float_iterator, float_iterator> > it;

for( it = vertex.PositionBegin() ; it != vertex.PositionEnd() ; ++it)

{

pair<float_iterator, float_iterator> coords;

float_iterator iCoord;

for(iCoord = coords.first ; iCoord != coords.last ; ++iCoord)

{

}

}

This will probably also require me to create my own highly special iterator class or is there a better way.

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I think I may help you, but your problem is not clear to me yet. On Wed, 15 Dec 2004, Eli Pulsifer wrote:

The first problem is depending on the format of the underling vertices, the stride between the data elements will change.

I didn't understand this. What is a stride between data elements? Why does it change? Why is that a problem?

The texture data not only has a stride but a variable number of elements. Some vertices have 2 texture coordinates, some 3, some even more.

Can't you have an internal container and return iterators to this container?

for( it = vertex.PositionBegin() ; it != vertex.PositionEnd() ; ++it) { pair<float_iterator, float_iterator> coords; float_iterator iCoord;

for(iCoord = coords.first ; iCoord != coords.last ; ++iCoord) { } }

It looks like 'it' is not being used inside the loop, so I don't understand this example. Let me tell you why I think I may help you. I have written an iterator adaptor that uses the elements through which the base iterator iterates in order to determine a range to be recursively iterated. An example: int[] a1 = {1,2,3}; int[] a2 = {4,5}; list<int> sublist1(a1, a1 + 3); list<int> sublist2(a2, a2 + 2); list<int*> l; l.push_back(sublist1); l.push_back(sublist2); nested_iterator<list<int*>::iterator>, range_getter> ni; for (ni = make_nested_iterator(l.begin(),l.end()); ni != make_nested_iterator(l.end(),l.end()); ni++) { // ni points successively to 1, 2, 3, 4, 5 } range_getter is an adaptable unary function class returning the begin(),end() range of the container passed to it. That is to say, a nested_iterator makes a bunch of ranges look as if they are one. Would this be helpful to you? Best, Rodrigo