Programming Forums > Application Development > C++

Kry1010 · Apr 5th, 2006, 8:39 AM

Hello,

I'm having problems with linking to a linked list within a linked list. I'm using two different structs within my class 'Players';

(Toggle Plain Text)

	class Players
{
 private:
        struct playerRec
	{
		char name[25];
		int age;
		int goals;
		struct historyRec* historyPtr;
		struct playerRec* next;
	};

	struct playerRec startPtr;

	struct historyRec
	{
		char club[25];
		int dateJoined;
		int dateLeft;
		struct historyRec* next;
	};
};

Setting up players is working fine, i.e. making a new playerRec node and assigning each of the fields/elements and linking those to other playerRec nodes is fine, the problem i'm having however is creating a new node for the 'historyPtr' to point to, this may help you to understand what I'm saying:

I can create a new 'historyRec' node using;

(Toggle Plain Text)

struct historyRec* tmpPtr = new struct historyRec;

but when I try to tell 'historyPtr' (in my playerRec) to point to this new node using the following code:

(Toggle Plain Text)

startPtr->historyPtr = tmpPtr

I get the following error - "Cannot convert from struct Players::historyRec * to struct historyRec*"

Likewise when I try the following:

(Toggle Plain Text)

 startPtr->historyPtr = new struct historyRec;

Sorry if this is something really simple I have overlooked, I'm fairly new programming especially linked lists.

Can anyone see what I'm missing/doing wrong, any help would be greatly
appreciated, many thanks.

Xyhm · Apr 5th, 2006, 9:03 AM

First you declare startPtr as "struct playerRec startPtr;" (i.e, a non-pointer), then you try to use it as a pointer with "startPtr->historyPtr = tmpPtr".

The declaration should either be "struct playerRec * startPtr" (and then of course then you need to fill that pointer with the appropriate struct), or the assignments to startPtr should be in the form "startPtr.historyPtr = tmpPtr". That is, with "." and not "->".

Or at least that's what I think after a fairly quick look.

Kry1010 · Apr 5th, 2006, 9:16 AM

Sorry, I missed out the asterisk when I manually entered some the code I wasn't originally going to show, but can you see any problems with it still?

Animatronic · Apr 5th, 2006, 10:14 AM

(Toggle Plain Text)

	class Players
{
 private:
        struct playerRec
	{
		char name[25];
		int age;
		int goals;
		struct historyRec* historyPtr;
		struct playerRec* next;
	};

	struct playerRec startPtr;

	struct historyRec
	{
		char club[25];
		int dateJoined;
		int dateLeft;
		struct historyRec* next;
	};
};

These are forward declarations for a struct named historyRec, your historyRec has the full name Players::historyRec.

In C to reffer to a struct you would do struct historyRec, in C++ the struct part isnt needed, as historyRec is a new type, and is only used like this todo forward declarations.

To fix your problem change struct historyRec to just historyRec (this may not work havent checked) or Players::historyRec.

Also you will probably have to move the definition for historyRec above playerRec (or use a forward declaration

).

The Dark · Apr 5th, 2006, 10:46 AM

I'm pretty sure to get that to complile, you must have another historyRec struct declaration around somewhere. Possibly you have a forward declaration that is not in the class. Put the forward declaration in the class.

Kry1010 · Apr 6th, 2006, 5:16 AM

Thanks a lot Animatronic, I tried what you said and it works now... I'm so happy :banana:

nnxion · Apr 6th, 2006, 6:21 AM

Most use a typedef for structs so one doesn't have to do it in C either.

Apr 5th, 2006, 8:39 AM	#1
Kry1010 Newbie Join Date: Apr 2006 Location: UK Posts: 3 Rep Power: 0	Linking to a linked list within a linked list Hello, I'm having problems with linking to a linked list within a linked list. I'm using two different structs within my class 'Players'; (Toggle Plain Text) class Players { private: struct playerRec { char name[25]; int age; int goals; struct historyRec* historyPtr; struct playerRec* next; }; struct playerRec startPtr; struct historyRec { char club[25]; int dateJoined; int dateLeft; struct historyRec* next; }; }; class Players { private: struct playerRec { char name[25]; int age; int goals; struct historyRec* historyPtr; struct playerRec* next; }; struct playerRec startPtr; struct historyRec { char club[25]; int dateJoined; int dateLeft; struct historyRec* next; }; }; Setting up players is working fine, i.e. making a new playerRec node and assigning each of the fields/elements and linking those to other playerRec nodes is fine, the problem i'm having however is creating a new node for the 'historyPtr' to point to, this may help you to understand what I'm saying: I can create a new 'historyRec' node using; (Toggle Plain Text) struct historyRec* tmpPtr = new struct historyRec; struct historyRec* tmpPtr = new struct historyRec; but when I try to tell 'historyPtr' (in my playerRec) to point to this new node using the following code: (Toggle Plain Text) startPtr->historyPtr = tmpPtr startPtr->historyPtr = tmpPtr I get the following error - *"Cannot convert from struct Players::historyRec to struct historyRec"* Likewise when I try the following: (Toggle Plain Text) startPtr->historyPtr = new struct historyRec; startPtr->historyPtr = new struct historyRec; Sorry if this is something really simple I have overlooked, I'm fairly new programming especially linked lists. Can anyone see what I'm missing/doing wrong, any help would be greatly appreciated, many thanks.

Apr 5th, 2006, 9:03 AM	#2
Xyhm Programmer Join Date: Mar 2006 Posts: 60 Rep Power: 3	First you declare startPtr as "struct playerRec startPtr;" (i.e, a non-pointer), then you try to use it as a pointer with "startPtr->historyPtr = tmpPtr". The declaration should either be "struct playerRec * startPtr" (and then of course then you need to fill that pointer with the appropriate struct), or the assignments to startPtr should be in the form "startPtr.historyPtr = tmpPtr". That is, with "." and not "->". Or at least that's what I think after a fairly quick look. Last edited by Xyhm; Apr 5th, 2006 at 9:16 AM.

Apr 5th, 2006, 10:14 AM	#4
Animatronic Programmer Join Date: Jun 2005 Posts: 99 Rep Power: 4	(Toggle Plain Text) class Players { private: struct playerRec { char name[25]; int age; int goals; struct historyRec* historyPtr; struct playerRec* next; }; struct playerRec startPtr; struct historyRec { char club[25]; int dateJoined; int dateLeft; struct historyRec* next; }; }; class Players { private: struct playerRec { char name[25]; int age; int goals; struct historyRec* historyPtr; struct playerRec* next; }; struct playerRec startPtr; struct historyRec { char club[25]; int dateJoined; int dateLeft; struct historyRec* next; }; }; These are forward declarations for a struct named historyRec, your historyRec has the full name Players::historyRec. In C to reffer to a struct you would do struct historyRec, in C++ the struct part isnt needed, as historyRec is a new type, and is only used like this todo forward declarations. To fix your problem change struct historyRec to just historyRec (this may not work havent checked) or Players::historyRec. Also you will probably have to move the definition for historyRec above playerRec (or use a forward declaration ).

Apr 6th, 2006, 6:21 AM	#7
nnxion Programming Guru Join Date: Jun 2005 Location: elemental plane Posts: 1,429 Rep Power: 5	Most use a typedef for structs so one doesn't have to do it in C either. __________________ "Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." -- Socrates

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Apr 5th, 2006, 9:16 AM	#3
Kry1010 Newbie Join Date: Apr 2006 Location: UK Posts: 3 Rep Power: 0	Sorry, I missed out the asterisk when I manually entered some the code I wasn't originally going to show, but can you see any problems with it still?

Apr 5th, 2006, 10:46 AM	#5
The Dark Expert Programmer Join Date: Jun 2005 Posts: 825 Rep Power: 4	I'm pretty sure to get that to complile, you must have another historyRec struct declaration around somewhere. Possibly you have a forward declaration that is not in the class. Put the forward declaration in the class.

Apr 6th, 2006, 5:16 AM	#6
Kry1010 Newbie Join Date: Apr 2006 Location: UK Posts: 3 Rep Power: 0	Thanks a lot Animatronic, I tried what you said and it works now... I'm so happy :banana:

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Programming Forums > Application Development > C++

Linking to a linked list within a linked list