Question

I have structure like this:

struct Rz3DContourNode {
  float x;
  float y;
  float z;
  float nx;
  float ny;
  float nz;
};

And I store elements in a STL vector as follows :

 std::vector < Rz3DContourNode >  nodes;

Now I want to change the nx,ny compoent of the nodes in the vector.I tried as follows:

*(&nodes[i].nx)=newNXValue;
*(&nodes[i].ny)=newNYValue;
*(&nodes[i].nz)=newNZValue;

This did not work.Is it because nodes[i] returns a copy of the object?

Is there any solution for this expect using pointers ?

I cannot use pointer (Rz3DContourNode*) , because I am using this vector in OpenGL as

glNormalPointer(GL_FLOAT,sizeof(Rz3DContourNode), &nodes[0].nx);

EDIT – I am sorry.I actually keep a QList and get the std::vector everytime.That was the reason

std::vector<Rz3DContourNode> nodeVector = nodes.toVector().toStdVector();

Answer 1

It works on my compiler….
Taking the address of the instance and then dereferencing it is the same as not doing it all.
So you don’t need it. So replace this

*(&nodes[i].nx)=newNXValue;

with

nodes[i].nx = newNXValue;

Here is the code sample I tried:

#include "stdafx.h"
#include <stdio.h>
#include <vector>

struct Rz3DContourNode {
  float x;
  float y;
  float z;
  float nx;
  float ny;
  float nz;
};

int _tmain(int argc, _TCHAR* argv[])
{
    std::vector < Rz3DContourNode >  nodes;
    float newNXValue = 4545.4f;
    float newNYValue = 453.0f;
    float newNZValue = 34.0f;

    for (int i = 0; i < 3; i++)
    {
        Rz3DContourNode node = {1.0f,1.0f,1.0f,1.0f,1.0f,1.0f};
        nodes.push_back(node);
    }

    for (int i = 0; i < nodes.size(); i++)
    {
        nodes[i].nx = newNXValue;
        nodes[i].ny = newNYValue;
        nodes[i].nz = newNZValue;
    }

    return 0;
}