C Declaration of reference variable requires an initializer?-CodePudding

I have a pointer / dereferencing issue where I'm getting the error:

Declaration of reference variable requires an initializer

With the following:

CastInfo& out;
if(SegmentCast(mOwner->GetGame()->GetPlayer(), mLineSegment, out))
{

This SegmentCast function is defined with the following parameters:

bool SegmentCast(Actor* actor, const LineSegment& l, CastInfo& outInfo)

and CastInfo is defined as:

struct CastInfo
{
    // Point of collision
    Vector3 mPoint;
    // Normal at collision
    Vector3 mNormal;
    // Owning actor you collided with
    class Actor* mActor = nullptr;
};

Because there's no constructor, I can't initialize out by doing CastInfo& out = CastInfo(), and yet I don't know how else to call that SegmentCast function with the CastInfo output.

How can I properly call this function with this reference variable?

CodePudding user response：

2 issues with this code

CastInfo& out;
if(SegmentCast(mOwner->GetGame()->GetPlayer(), mLineSegment, out))
{

First you actually have to have an instance of CastInfo somewhere that can be referenced in that call to SegmentCast

Second you cannot create a refernce thats not bound to an actual object (unlike a pointer)

If you want a local instance do

 CastInfo out;
 if(SegmentCast(mOwner->GetGame()->GetPlayer(), mLineSegment, out))
 {

This creates a local stack instance, a reference to it will be passed (you dont have to do anything else, the compiler knows thats what the function wants)

Or if you need a heap instance do

CastInfo *out= new CastInfo();
if(SegmentCast(mOwner->GetGame()->GetPlayer(), mLineSegment, *out))
{

This makes a pointer to a heap object. To pass it to the function you need to derference it (*out) and then the compiler will pass it as a reference (just like the first example)

Ideally you would use std::unique_ptr rather than a raw new and pointer. If you do not, then remeber to delete out once you are done

CodePudding user response：

Be wary of analogies between pointers and references; that will usually be confusing. A pointer can point to nowhere; a reference always refers to an object. So, while you can write CastInfo* out;, which creates a pointer with an unspecified value, you cannot write CastInfo& out;; it is simply not allowed. If you need to create a reference there must be an object that it refers to:

CastInfo info;
CastInfo& out = info;