reference to address of stack object

Question

I am having difficulty understanding why below code does not compile under Visual Studio 2012, error already embedded in below code. I feel it has something to do with referencing stack object, but not quite sure. Can someone help?

Thanks

#include <iostream>

typedef struct Node {
    Node *next;
} Node;

void test(Node *&p) {
    p=p->next;
}

void main() {
    Node *p1=new Node();
    test(p1);   // this line compiles okay

    Node p={0};
    test(&p);    // error C2664: 'test' : cannot convert parameter 1 from 'Node *' to 'Node *&'
}

Gcc gives you a good diagnostic: "error: invalid initialization of non-const reference of type ‘Node*&’ from an rvalue of type ‘Node"* And answers your doubt competently. — Alok Save
– Alok Save, Commented Apr 2, 2013 at 6:34
Lol. Its deja-vu all over again.=P. The gcc error is about as concrete as you can get. The function is expecting a reference to an lvalue. You're passing an rvalue. There is no "there" there, so to speak. — WhozCraig
– WhozCraig, Commented Apr 2, 2013 at 6:36

Alexey Frunze · Accepted Answer · 2013-04-02 06:30:24Z

2

&p is not a variable of type Node*. It's a constant of type Node*.

Even if you could somehow take a reference to p and pass it to test(), p=p->next; would still fail because you can't assign to a constant.

answered Apr 2, 2013 at 6:30

Alexey Frunze

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2 Comments

Alexey Frunze Over a year ago

@Cheersandhth.-Alf Thanks! I just started wondering what was wrong.

WhozCraig Over a year ago

I'm guessing the down-voter was thinking something about the phrase "r-value" when he pulled the trigger.

maditya · Accepted Answer · 2013-04-02 06:32:15Z

1

You're passing a variable by address, not a pointer to a variable by reference. I think this will work:

void main() {
    Node *p1=new Node();
    test(p1);   

    Node p={0};
    Node* p2 = &p;
    test(p2);     
}

answered Apr 2, 2013 at 6:32

maditya

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