Question

Just started programming in C++.

I’ve created a Point class, a std::list and an iterator like so:

class Point {  public:     int x, y;     Point(int x1, int y1)     {         x = x1;         y = y1;     } };  std::list <Point> pointList; std::list <Point>::iterator iter; 

I then push new points onto pointList.

Now, I’m needing to iterate through all the points in pointList, so I need to loop using the iterator. This is where I get screwed up.

for(iter = pointList.begin(); iter != pointList.end(); iter++) {     Point currentPoint = *iter;     glVertex2i(currentPoint.x, currentPoint.y); } 

---

Update

You guys were right, the problem isn’t in my iterating the list. It appears the problem is when I am attempting to push something on to the list.

Exact error:

mouse.cpp: In function void mouseHandler(int, int, int, int)': mouse.cpp:59: error: conversion fromPoint*’ to non-scalar type `Point’ requested

Those lines are:

 if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {     Point currentPoint = new Point(x, y);     pointList.push_front(currentPoint);  } 

What does it conversion between Point* to non-scalar type Point? I’m just trying to create new points and push them onto the list here.

Answer 1

That should be a valid bit of code.

#include <iostream> #include <list>  class Point {  public:     int x, y;     Point(int x1, int y1)     {         x = x1;         y = y1;     } };  int main() {     std::list<Point> points;      points.push_back(Point(0, 0));     points.push_back(Point(1, 1));     points.push_back(Point(2, 2));      std::list<Point>::iterator iter;      for(iter = points.begin(); iter != points.end(); ++iter)     {         Point test = *iter;         std::cout << test.x << ', ' << test.y << '; ';     }     std::cout << std::endl;      return 0; } 

Using this code:

jasons-macbook41:~ g++ test.cpp jasons-macbook41:~ ./a.out 0, 0; 1, 1; 2, 2;  jasons-macbook41:~  

Although I wouldn’t create a temporary copy of the Point as your code does. I’d rewrite the loop like this:

for(iter = points.begin(); iter != points.end(); ++iter) {     std::cout << iter->x << ', ' << iter->y << '; '; } 

An iterator is syntactically similar to a pointer.

EDIT: Given your new problem, drop the ‘new’ from the construction line. That’s creating a pointer to a Point, as opposed to a Point on the stack. This would be valid:

Point* temp = new Point(0, 0); 

Or this:

Point temp = Point(0, 0); 

And you’d be better off with the latter.