Question

I’m having a newbie problem in C++.
I have a struct Edge defined as following:

struct Edge {
    int position[4];
    int average;
};

Now I need to create a lot of these structs and I created a helper-method for that, that creates an array of these structs based on some parameters:

Edge* createEdges(int some_parameters){
    Edge *edges = new Edge[8];

    for(int i = 0 ; i < 8; i++){
        Edge edge;
        edge.position[0] = 1; //fill the rest of the edge array in the same manner
        edge.average = 10;

        edges[i] = edge;
    }

    return edges;
}

However when I now call: Edge *edges = createEdges(int some_parameters) there is no sensible data in the Edge array (out of scope?).

I think I’m mixing up some things here but I would prefer if I can make this work without resorting to the vector datastructures. Is this the normal way of handling this or should I declare the edge array myself and pass it to the helper method to fill it up?

Edit:

First of all, I want to thank everyone for there comments/hints/tips/advice/… they have helped me to find the problem that I overlooked so easily.
After I seen the replies that the code should work, I tested the simplified code aswell (something I should have done in the 1st place) and surprisingly, it worked! So then I checked to see why my real code didn’t work and the simplified version did.
My real code looked like this:

Edge* createEdges(int some_parameters){
     Edge* edges = new Edge[8];
     if(some_parameter != 0){
          //create the edges as in my 1st snippet
          return NULL; //doh, should return edges here !
     } else { 
          return NULL;
     }
}

The reason why I had not seen that I simply returned the wrong value (NULL) was because the debugger showed me some 0xf6f6f6 addressess with some negative values for edge.position (something I don’t quite understand, it should’ve just show me 0x000000, perhaps I was just imagining things).

All in all, this was an important lesson in why to never code after 3am, nothing good will come of it!

Answer 1

Here is a bit modified version that creates edges in the function, and returns a vector containing all created edges.

#include <iostream>
#include <vector>

struct Edge {
    int position[4];
    int average;
};

std::vector< Edge > createEdges(int some_parameters){
    std::vector< Edge > edges( 8 );

    for(int i = 0 ; i < 8; i++){
        const Edge edge{ { 1, 0, 0, 0 }, 10 };

        edges[i] = edge;
    }

    return edges;
}


int main()
{
    auto e( createEdges(5));

    std::cout<<e[0].average<<std::endl;
}

There are few modifications :

1. Instead of allocating an array of edges, and returning pointer, I return vector
2. the way edge objects are created, and initialized (I think this is what is asked)