push_back(new triangle)

Question

In C++ by FLTK, to define a circle we use some code like this:

Circle c(Point(x,y), r);

And we can using vector_ref put and save them in a vector, like:

Vector_ref<Circle> vc;
vc.push_back(new Circle(Point(x,y),r));

OK, those were about Circle and no problem till now! Triangle can be defined like this for using in codes:

Graph_lib::polygon poly;
poly.add(Point(x1,y1),r1);
poly.add(Point(x2,y2),r2);
poly.add(Point(x3,y3),r3);

and this is a vector to saving them:

Vector_ref<Graph_lib::Polygon> vp;

The problem is that how to save/put triangles/polygons into that vp vector using new keyword like the circle does?

The code I used as an answer to the exercise no 12 (of here) is this:

/* The binary-tree class, one of the topics that has been said in Programming Principles and Practice using C++ book by Biarne Stroustrup.
   This code is written by R Abbasi (s.rabbasi@yahoo.com) */
#include <Simple_window.h>
#include <iostream>

vector <Graph_lib::Polygon> vpo;
vector <Point> vp;
int pow(int);

class Binary_tree: public Shape {
public:
    Binary_tree(Point _p, int l):level(l), p(_p) {  
        preparing(); }

    void preparing();
    void put_nodes(Point);
    void wheel(Point);
    void make_nodes(Point);
    void draw_lines() const {
        for(int i = 0; i*2+2 < vp.size(); i++) {
            fl_line(vp[i].x,vp[i].y,  vp[i*2+1].x,vp[i*2+1].y);
            fl_line(vp[i].x,vp[i].y,  vp[i*2+2].x,vp[i*2+2].y);
        }
    }

private:
    Point p;
    int i, j, k, level;
    double scale;
};
//**********************************

void Binary_tree::preparing() {
    if(level < 1) error("Bad inputted level!");
    else if (level == 1) put_nodes(p);
    else {
        scale = 5 * pow(level); 
        i = 1; j = 1; k = 3; 
        put_nodes(p); 
        make_nodes(p);
    }
}

//***************************************

void Binary_tree::put_nodes(Point p) { 
    vp.push_back(p);
    Graph_lib::Polygon poly;
    poly.add(Point(p.x-2,p.y));
    poly.add(Point(p.x,p.y-3));
    poly.add(Point(p.x+3,p.y));

    vpo.push_back(&poly);
}

//******************************************

void Binary_tree::wheel(Point p) {
    put_nodes(Point(p.x - scale, p.y+30));
    put_nodes(Point(p.x + scale, p.y+30));
}

//*****************************************

void Binary_tree::make_nodes(Point p) {
    while(vp.size() < (pow(k)-1))
        wheel(vp[vp.size()-i++]);

    if(i < pow(level)) {
        k++;
        scale *= 1.0/2.0;
        make_nodes(vp[vp.size()-i]);
    }
}

//*********************

int pow(int l)  {
    int m = 2; 
    for(int k = 2; k < l; k++) m *= 2; 
    return m;
}

//***************************************

int main() try
{
    Simple_window win(Point(),1300,500, "Binary_tree");
    int level;
    cout<< "Please enter the level of the Binary-tree:";
    if(!(cin>>level)) error("Bad number of level!");

    Point p(10*pow(level),20);
    Binary_tree b_t(p,level);

    vpo[0].set_color(Color::red);
    vpo[0].set_style(Line_style(Line_style::solid,3));
        win.attach(vpo[0]);
    for(int i=1; i<vpo.size(); i++) {
        vpo[i].set_color(Color::blue);
        win.attach(vpo[i]);
    }
    win.attach(b_t);
    win.wait_for_button();
    return 0;
}

//*****************************

catch(exception& e) {
    cerr << e.what() << "\n\a";
    return 0;
}

And errors are:

*Error 9 error C2664: 'void std::vector<_Ty>::push_back(Graph_lib::Polygon &&)' : cannot convert parameter 1 from 'Graph_lib::Polygon *' to 'Graph_lib::Polygon &&' c:\users\cs\documents\visual studio 2012\projects\test_1\test_1\test_1.cpp 53

14 IntelliSense: no instance of overloaded function "std::vector<_Ty, _Alloc>::push_back [with _Ty=Graph_lib::Polygon, _Alloc=std::allocator]" matches the argument list argument types are: (Graph_lib::Polygon ) object type is: std::vector> c:\Users\CS\Documents\Visual Studio 2012\Projects\test_1\test_1\test_1.cpp 53

Answer 1

For Vector_ref<polygon> (using new)

From what I understand of Vector_ref, this is simply a std::vector with pointers and code to clean up the dynamically allocated memory at the end. This means you must use new to allocate your polygon. So, if you must use new, you can create your polygon first (using new) and then push it:

// Create your new polygon
polygon* poly = new polygon;
poly->add(Point(...));
poly->add(...);
poly->add(...);

// Push that polygon into the vector
vp.push_back(poly);

For std::vector<polygon*> (taking the address)

If the polygon doesn't go out of scope (i.e. you don't leave the function or pass a }) you can take the address of the polygon:

// Create polygon
polygon poly;
poly.add(...); // by 3

// Add the polygon to the vector
vp.push_back(&poly);

For std::vector<polygon> (making a copy)

If the vector is not an array of pointers, which is the case for std::vector<polygon> (but not for std::vector<polygon*> or Vector_ref<polygon>), then you should not use new or &. Instead if you just use push_back of the vector with the polygon, the polygon will be copied into the vector.

// Create your new polygon
polygon poly;
poly.add(...); // by 3

// Copy the polygon into the vector
vp.push_back(poly);