How do I initiliaze a head in a doubly-linked list to be NULL?

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I have a homework to implement a doubly-linked list in C++ with two structs. One of them should hold the next and previous pointers, as well as the data. The other struct should hold two pointers, one for the head and one for the tail

Struct DlistElem
 int data;
 DlistElem* next;
 DlistElem* prev;
 

Struct Dlist
 Dlist * head;
 Dlist * tail;


//some functions

the problem I'm having is I don't know how to initialize both the head and tail to be null in order to use them. Any help would be greatly appreciated!

asked Nov 10 at 23:03

Tonislav Tachev

3

What is wrong with assigning NULL to each?
– Scott Hunter
Nov 10 at 23:06

Hey Scott, thanks for the answer. I'm quite new to C++ so I didn't know if this was allowed :)
– Tonislav Tachev
Nov 10 at 23:10

Usually, the best choice for C++ is nullptr , a literal since C++11.
– 2785528
Nov 10 at 23:23

See also: stackoverflow.com/a/177007/2785528
– 2785528
Nov 10 at 23:48

add a comment |

up vote
0
down vote

favorite

Struct DlistElem
 int data;
 DlistElem* next;
 DlistElem* prev;
 

Struct Dlist
 Dlist * head;
 Dlist * tail;


//some functions

the problem I'm having is I don't know how to initialize both the head and tail to be null in order to use them. Any help would be greatly appreciated!

asked Nov 10 at 23:03

Tonislav Tachev

3

What is wrong with assigning NULL to each?
– Scott Hunter
Nov 10 at 23:06

Hey Scott, thanks for the answer. I'm quite new to C++ so I didn't know if this was allowed :)
– Tonislav Tachev
Nov 10 at 23:10

Usually, the best choice for C++ is nullptr , a literal since C++11.
– 2785528
Nov 10 at 23:23

See also: stackoverflow.com/a/177007/2785528
– 2785528
Nov 10 at 23:48

add a comment |

up vote
0
down vote

favorite

Struct DlistElem
 int data;
 DlistElem* next;
 DlistElem* prev;
 

Struct Dlist
 Dlist * head;
 Dlist * tail;


//some functions

the problem I'm having is I don't know how to initialize both the head and tail to be null in order to use them. Any help would be greatly appreciated!

asked Nov 10 at 23:03

Tonislav Tachev

Struct DlistElem
 int data;
 DlistElem* next;
 DlistElem* prev;
 

Struct Dlist
 Dlist * head;
 Dlist * tail;


//some functions

the problem I'm having is I don't know how to initialize both the head and tail to be null in order to use them. Any help would be greatly appreciated!

c++

asked Nov 10 at 23:03

Tonislav Tachev

asked Nov 10 at 23:03

Tonislav Tachev

asked Nov 10 at 23:03

Tonislav Tachev

asked Nov 10 at 23:03

Tonislav Tachev

asked Nov 10 at 23:03

Tonislav Tachev

3

What is wrong with assigning NULL to each?
– Scott Hunter
Nov 10 at 23:06

Hey Scott, thanks for the answer. I'm quite new to C++ so I didn't know if this was allowed :)
– Tonislav Tachev
Nov 10 at 23:10

Usually, the best choice for C++ is nullptr , a literal since C++11.
– 2785528
Nov 10 at 23:23

See also: stackoverflow.com/a/177007/2785528
– 2785528
Nov 10 at 23:48

add a comment |

3

What is wrong with assigning NULL to each?
– Scott Hunter
Nov 10 at 23:06

Hey Scott, thanks for the answer. I'm quite new to C++ so I didn't know if this was allowed :)
– Tonislav Tachev
Nov 10 at 23:10

Usually, the best choice for C++ is nullptr , a literal since C++11.
– 2785528
Nov 10 at 23:23

See also: stackoverflow.com/a/177007/2785528
– 2785528
Nov 10 at 23:48

What is wrong with assigning NULL to each?
– Scott Hunter
Nov 10 at 23:06

Hey Scott, thanks for the answer. I'm quite new to C++ so I didn't know if this was allowed :)
– Tonislav Tachev
Nov 10 at 23:10

Usually, the best choice for C++ is nullptr , a literal since C++11.
– 2785528
Nov 10 at 23:23

See also: stackoverflow.com/a/177007/2785528
– 2785528
Nov 10 at 23:48

add a comment |

3 Answers
3

active

oldest

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up vote
0
down vote

Initialize the pointers with NULL when you create a DlistElem and Dlist.

struct DlistElem
 DlistElem* prev;
 DlistElem* next;
 int data;
 DlistElem() :
 prev(NULL),
 next(NULL),
 data()
 


struct Dlist
 Dlist* head;
 Dlist* tail;
 Dlist() :
 head(NULL),
 tail(NULL)

answered Nov 10 at 23:09

Ted Lyngmo

1,795315

add a comment |

up vote
0
down vote

Another way this can be done in c++11 is:

struct DlistElem
 int data;
 DlistElem* next = nullptr;
 DlistElem* prev = nullptr;


struct Dlist
 Dlist * head = nullptr;
 Dlist * tail = nullptr;

answered Nov 11 at 0:35

Patrick

808

add a comment |

up vote
0
down vote

I don't know how to initialize both the head and tail to be null in order to use them.

struct DlistElem 
 int data;
 DlistElem* next;
 DlistElem* prev;

 DlistElem() : data, next, prev
 
;

struct DlistElem 
 int data;
 DlistElem* next;
 DlistElem* prev;
;

edited Nov 11 at 5:23

answered Nov 10 at 23:14

Swordfish

One thing I forgot to mention is, how do I later on access it some methods ?
– Tonislav Tachev
Nov 10 at 23:30

@TonislavTachev What is "on access it some methods ?" ?
– Swordfish
Nov 11 at 5:23

@TonislavTachev The same way you access all other struct members? Not sure what your problem is.
– Fei Xiang
Nov 11 at 5:26

Since I want to use the head in let's say an InsertAtFirst() method, where I first check if the head is null, afterwards if it is I'll proceed to add a new node. But I'm getting an error message, saying that head wasn't defined in this scope
– Tonislav Tachev
Nov 11 at 11:07

@TonislavTachev comments are not for questions. if you have another question, go and ask another question.
– Swordfish
Nov 11 at 11:23

add a comment |

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

up vote
0
down vote

Initialize the pointers with NULL when you create a DlistElem and Dlist.

struct DlistElem
 DlistElem* prev;
 DlistElem* next;
 int data;
 DlistElem() :
 prev(NULL),
 next(NULL),
 data()
 


struct Dlist
 Dlist* head;
 Dlist* tail;
 Dlist() :
 head(NULL),
 tail(NULL)

answered Nov 10 at 23:09

Ted Lyngmo

1,795315

add a comment |

up vote
0
down vote

Initialize the pointers with NULL when you create a DlistElem and Dlist.

struct DlistElem
 DlistElem* prev;
 DlistElem* next;
 int data;
 DlistElem() :
 prev(NULL),
 next(NULL),
 data()
 


struct Dlist
 Dlist* head;
 Dlist* tail;
 Dlist() :
 head(NULL),
 tail(NULL)

answered Nov 10 at 23:09

Ted Lyngmo

1,795315

add a comment |

up vote
0
down vote

Initialize the pointers with NULL when you create a DlistElem and Dlist.

struct DlistElem
 DlistElem* prev;
 DlistElem* next;
 int data;
 DlistElem() :
 prev(NULL),
 next(NULL),
 data()
 


struct Dlist
 Dlist* head;
 Dlist* tail;
 Dlist() :
 head(NULL),
 tail(NULL)

answered Nov 10 at 23:09

Ted Lyngmo

1,795315

Initialize the pointers with NULL when you create a DlistElem and Dlist.

struct DlistElem
 DlistElem* prev;
 DlistElem* next;
 int data;
 DlistElem() :
 prev(NULL),
 next(NULL),
 data()
 


struct Dlist
 Dlist* head;
 Dlist* tail;
 Dlist() :
 head(NULL),
 tail(NULL)

answered Nov 10 at 23:09

Ted Lyngmo

1,795315

answered Nov 10 at 23:09

Ted Lyngmo

1,795315

answered Nov 10 at 23:09

Ted Lyngmo

1,795315

answered Nov 10 at 23:09

Ted Lyngmo

1,795315

add a comment |

up vote
0
down vote

Another way this can be done in c++11 is:

struct DlistElem
 int data;
 DlistElem* next = nullptr;
 DlistElem* prev = nullptr;


struct Dlist
 Dlist * head = nullptr;
 Dlist * tail = nullptr;

answered Nov 11 at 0:35

Patrick

808

add a comment |

up vote
0
down vote

Another way this can be done in c++11 is:

struct DlistElem
 int data;
 DlistElem* next = nullptr;
 DlistElem* prev = nullptr;


struct Dlist
 Dlist * head = nullptr;
 Dlist * tail = nullptr;

answered Nov 11 at 0:35

Patrick

808

add a comment |

up vote
0
down vote

Another way this can be done in c++11 is:

struct DlistElem
 int data;
 DlistElem* next = nullptr;
 DlistElem* prev = nullptr;


struct Dlist
 Dlist * head = nullptr;
 Dlist * tail = nullptr;

answered Nov 11 at 0:35

Patrick

808

Another way this can be done in c++11 is:

struct DlistElem
 int data;
 DlistElem* next = nullptr;
 DlistElem* prev = nullptr;


struct Dlist
 Dlist * head = nullptr;
 Dlist * tail = nullptr;

answered Nov 11 at 0:35

Patrick

808

answered Nov 11 at 0:35

Patrick

808

answered Nov 11 at 0:35

Patrick

808

answered Nov 11 at 0:35

Patrick

808

add a comment |

up vote
0
down vote

I don't know how to initialize both the head and tail to be null in order to use them.

struct DlistElem 
 int data;
 DlistElem* next;
 DlistElem* prev;

 DlistElem() : data, next, prev
 
;

struct DlistElem 
 int data;
 DlistElem* next;
 DlistElem* prev;
;

edited Nov 11 at 5:23

answered Nov 10 at 23:14

Swordfish

One thing I forgot to mention is, how do I later on access it some methods ?
– Tonislav Tachev
Nov 10 at 23:30

@TonislavTachev What is "on access it some methods ?" ?
– Swordfish
Nov 11 at 5:23

@TonislavTachev The same way you access all other struct members? Not sure what your problem is.
– Fei Xiang
Nov 11 at 5:26

Since I want to use the head in let's say an InsertAtFirst() method, where I first check if the head is null, afterwards if it is I'll proceed to add a new node. But I'm getting an error message, saying that head wasn't defined in this scope
– Tonislav Tachev
Nov 11 at 11:07

@TonislavTachev comments are not for questions. if you have another question, go and ask another question.
– Swordfish
Nov 11 at 11:23

add a comment |

up vote
0
down vote

I don't know how to initialize both the head and tail to be null in order to use them.

struct DlistElem 
 int data;
 DlistElem* next;
 DlistElem* prev;

 DlistElem() : data, next, prev
 
;

struct DlistElem 
 int data;
 DlistElem* next;
 DlistElem* prev;
;

edited Nov 11 at 5:23

answered Nov 10 at 23:14

Swordfish

One thing I forgot to mention is, how do I later on access it some methods ?
– Tonislav Tachev
Nov 10 at 23:30

@TonislavTachev What is "on access it some methods ?" ?
– Swordfish
Nov 11 at 5:23

@TonislavTachev The same way you access all other struct members? Not sure what your problem is.
– Fei Xiang
Nov 11 at 5:26

Since I want to use the head in let's say an InsertAtFirst() method, where I first check if the head is null, afterwards if it is I'll proceed to add a new node. But I'm getting an error message, saying that head wasn't defined in this scope
– Tonislav Tachev
Nov 11 at 11:07

@TonislavTachev comments are not for questions. if you have another question, go and ask another question.
– Swordfish
Nov 11 at 11:23

add a comment |

up vote
0
down vote

I don't know how to initialize both the head and tail to be null in order to use them.

struct DlistElem 
 int data;
 DlistElem* next;
 DlistElem* prev;

 DlistElem() : data, next, prev
 
;

struct DlistElem 
 int data;
 DlistElem* next;
 DlistElem* prev;
;

edited Nov 11 at 5:23

answered Nov 10 at 23:14

Swordfish

I don't know how to initialize both the head and tail to be null in order to use them.

struct DlistElem 
 int data;
 DlistElem* next;
 DlistElem* prev;

 DlistElem() : data, next, prev
 
;

struct DlistElem 
 int data;
 DlistElem* next;
 DlistElem* prev;
;

edited Nov 11 at 5:23

answered Nov 10 at 23:14

Swordfish

edited Nov 11 at 5:23

answered Nov 10 at 23:14

Swordfish

answered Nov 10 at 23:14

Swordfish

answered Nov 10 at 23:14

Swordfish

One thing I forgot to mention is, how do I later on access it some methods ?
– Tonislav Tachev
Nov 10 at 23:30

@TonislavTachev What is "on access it some methods ?" ?
– Swordfish
Nov 11 at 5:23

@TonislavTachev The same way you access all other struct members? Not sure what your problem is.
– Fei Xiang
Nov 11 at 5:26

Since I want to use the head in let's say an InsertAtFirst() method, where I first check if the head is null, afterwards if it is I'll proceed to add a new node. But I'm getting an error message, saying that head wasn't defined in this scope
– Tonislav Tachev
Nov 11 at 11:07

@TonislavTachev comments are not for questions. if you have another question, go and ask another question.
– Swordfish
Nov 11 at 11:23

add a comment |

One thing I forgot to mention is, how do I later on access it some methods ?
– Tonislav Tachev
Nov 10 at 23:30

@TonislavTachev What is "on access it some methods ?" ?
– Swordfish
Nov 11 at 5:23

@TonislavTachev The same way you access all other struct members? Not sure what your problem is.
– Fei Xiang
Nov 11 at 5:26

Since I want to use the head in let's say an InsertAtFirst() method, where I first check if the head is null, afterwards if it is I'll proceed to add a new node. But I'm getting an error message, saying that head wasn't defined in this scope
– Tonislav Tachev
Nov 11 at 11:07

@TonislavTachev comments are not for questions. if you have another question, go and ask another question.
– Swordfish
Nov 11 at 11:23

One thing I forgot to mention is, how do I later on access it some methods ?
– Tonislav Tachev
Nov 10 at 23:30

@TonislavTachev What is "on access it some methods ?" ?
– Swordfish
Nov 11 at 5:23

@TonislavTachev The same way you access all other struct members? Not sure what your problem is.
– Fei Xiang
Nov 11 at 5:26

Since I want to use the head in let's say an InsertAtFirst() method, where I first check if the head is null, afterwards if it is I'll proceed to add a new node. But I'm getting an error message, saying that head wasn't defined in this scope
– Tonislav Tachev
Nov 11 at 11:07

@TonislavTachev comments are not for questions. if you have another question, go and ask another question.
– Swordfish
Nov 11 at 11:23

add a comment |

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