Struct with Vector of Structs

Question

Sorry, the title sounds a little confusing, let me explain.

I have a struct, which has a vector of structs, like this:

struct foo {
int x;
vector < foo > bar;
};

But I get an error of "No Instance of Overloaded Method" when I try this syntax:

foo a;
foo b;
b.x = 3;
a.bar.push_back(b);

Basically, I am just trying to create a "relationship" between a and b, with bar being the relationship vector containing all related instances of foo.

Any suggestions?

Answer 1

Your code is, unfortunately, illegal according to the C++ Standard, because you are passing an incomplete type as a template parameter to the Standard Library, which is prohibited in general and std::vector doesn't have an exception to the general rule.

The Boost documentation has a great explanation.

You can either use a container which explicitly supports incomplete types, as the Boost ones do, or use std::vector<std::unique_ptr<foo>>, because the Standard says in 20.9.1p5:

The template parameter T of unique_ptr may be an incomplete type.

Answer 2

May be it's your compiler, Mine gives no error or warnings.

#include <iostream> 
#include <vector>
using namespace std;



struct foo {
int x;
vector < foo > bar;
};


int main()
{
foo a;
foo b;
b.x = 3;
a.bar.push_back(b);
cout<<a.bar[0].x;
    cout<<"\n";
return 0;
}