circular struct reference in c++

[lloopy]

I am trying to represent a map using nodes. This code segment seems to work just fine in C, but craps out in C++.

struct node{
char name[50];
struct node* neighbors[6];
};

struct node one;
struct node two;
struct node three;

struct node one={"one",
{&two, &three}
};

struct node two={"two",
{&one, &three}
};

struct node three={"three",
{&two, &one}
};
--------------------------
My problem is that when I try to do this in C++, I get complaints of redefinitions. If I don't do the forward declaration, then I get unknown object errors.

I'm fundamentally missing something, I'm sure.

-lloopy

[ravenspoint]

I am trying to represent a map using nodes. This code segment seems to work just fine in C, but craps out in C++.

struct node{
char name[50];
struct node* neighbors[6];
};

struct node one;
struct node two;
struct node three;

struct node one={"one",
{&two, &three}
};

struct node two={"two",
{&one, &three}
};

struct node three={"three",
{&two, &one}
};
--------------------------
My problem is that when I try to do this in C++, I get complaints of redefinitions. If I don't do the forward declaration, then I get unknown object errors.

I'm fundamentally missing something, I'm sure.

-lloopy

Why not use something like this:

strcpy(one.name, "one" );
one.neighbour[0] = &two;

and so on

[lloopy]

The code sample I included was a demonstration of the concept.

The actual structure is somewhat more complicated.

There are 120 nodes. Each node keeps a list of three types of neighbors, as well as 7 other pieces of information.

This seems more cumbersome:
------------------
node1.neighbor_ type1[0]=&node2;
node1.neighbor_ type1[1]=&node3;
node1.neighbor_ type1[2]=&node4;

node1.neighbor_ type2[0]=&node2;
node1.neighbor_ type2[1]=&node5;

node1.neighbor_ type3[0]=&node3;
node1.neighbor_ type3[1]=&node6;

node1.size=1;
node1.type=3;
node1.strength= 6;
node1.owner=&Bo b;

------------------------------
than this:
=============== ======
struct node node1={"node1",
{&node2,&node3, &node4},
{&node2,&node5} ,
{&node3,&node6} ,
1,3,6,&Bob
};
=============== =======
...which worked just fine in C.

[ravenspoint]

You should consider making your node a class, with a constructor and assignment methods. Properly designed, this would allow you to initialize everything with a minimum of cumber.
[CODE=cpp]
class node {

...


setNeighbour1( node& n1,
node& n2,
node& n3 );
};
[/CODE]

[JosAH]

I am trying to represent a map using nodes. This code segment seems to work just fine in C, but craps out in C++.

struct node{
char name[50];
struct node* neighbors[6];
};

struct node one;
struct node two;
struct node three;

struct node one={"one",
{&two, &three}
};

struct node two={"two",
{&one, &three}
};

struct node three={"three",
{&two, &one}
};
--------------------------
My problem is that when I try to do this in C++, I get complaints of redefinitions. If I don't do the forward declaration, then I get unknown object errors.

I'm fundamentally missing something, I'm sure.

-lloopy

C++ considers them redefinitions because first you (tentatively) defined, say,
your struct one as

[code=cpp]
struct node one;
[/code]

and a few line below you redefine (and initialize) it as follows:

[code=cpp]
struct node one={"one",
{&two, &three}
};
[/code]

An old C trick can be this:

[code=cpp]
extern struct node one;
extern struct node two;
extern struct node three;
[/code]

This turns the three in just declarations.

kind regards,

Jos

[lloopy]

Thanks for the help. I started rearchitecting my code, but decided that simply using extern would fix the issue.

[weaknessforcats]

C++ considers them redefinitions because first you (tentatively) defined, say,
your struct one as


Code: ( cpp )
struct node one;

or just omit the struct keyword:

[code=cpp]
node one; //calls default constructor
[/code]

This is C++ and not C and this is one place where the two languages part company.