Question

Anyone knows how to initialize a reference in a dynamically allocated structure?
or why this doesnt work?

#include <stdio.h>
#include <stdlib.h>

class A
{

};

struct S
{
    A& a;
};

int main()
{
    A a;

    S* s=new S;
    s->a=a;

    printf("a addr:%p\n", &a);
    printf("s->a addr:%p\n", &(s->a));
delete s;
    return 0;
}

output:

a addr:0x7fff95b65aaf
s->a addr:(nil)

Answer 1

You need to initialize reference members within the initializer list of a constructor. Even the body of the constructor is too late, because the member has already been initialized, and can’t be changed.

In your code, you are using the (compiler-provided) default constructor, and then trying to set the reference after the object has been constructed.

Try this:

struct S
{
    S(A& a_) : a(a_){} 
    A& a;
};

int main()
{
    A a;

    S* s=new S(a);
...