How can I create a dynamically sized array of linked lists?

Question

I need to create an array of linked lists at runtime for a hash table assignment. The sample code that we are given only allows for creating arrays of static size, and I cannot figure out how to modify it to work with a variable, as everything I have tried has resulted in errors.

Sample Code:

typedef std::list<int> INT_LIST;
typedef INT_LIST* INT_LIST_POINTER;
int size = 13;
INT_LIST_POINTER myArray[size];
INT_LIST_POINTER tmpPtr;
// initialize the array to point to empty lists
for (int i=0; i<size; i++){
tmpPtr = new INT_LIST;
myArray[i] = tmpPtr;
}

My Current, nonworking Code:

typedef std::list<int> INT_LIST;
typedef INT_LIST* INT_LIST_POINTER;
INT_LIST_POINTER myArray = new INT_LIST[p];
INT_LIST_POINTER tmpPtr;
for (int i=0; i<n; i++){
INT_LIST* temp = new INT_LIST;
myArray[i] = temp;
}

The major problem seems to be with

myArray[i] =  temp;

which says nothing matches those operands.

check out std::vector.resize and std::vector.push_back methods. — Will Ness
– Will Ness, Commented Feb 29, 2012 at 9:25
If you want to wind up your teacher, point out that the sample code is not valid C++. It should be const int size = 13;. To demonstrate this, compile using for example GCC with the -pedantic-errors option to disable non-standard language extensions. — Steve Jessop
– Steve Jessop, Commented Feb 29, 2012 at 9:42
All uppercase identifiers are - by convention - used to denote template parameters when short (e.g. T, U, T2), otherwise preprocessor macros. They should not be used for types. A small matter, but enough to make me think whoever's given you your sample code doesn't have a clue. Further, why have an array of pointers to std::list when you can just have an array of std::list? It's less efficient and less maintainable (note - the deallocation code - another loop for delete - is missing from the sample). — Tony Delroy
– Tony Delroy, Commented Feb 29, 2012 at 10:04

Luchian Grigore · Accepted Answer · 2012-02-29 08:55:08Z

2

If this is C++, why not use std:

std::vector<std::list<MyClass> > x;

answered Feb 29, 2012 at 8:55

Luchian Grigore

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3 Comments

ereOn Over a year ago

This is obviously a good answer but the OP tagged the question "homework", so I wouldn't be surprised if he can't use anything inside std::.

Carl Davis Over a year ago

Forgot to include these two lines typedef std::list<int> INT_LIST; typedef INT_LIST* INT_LIST_POINTER;

Will Ness Over a year ago

@ereOn he uses std::list so std::vector<INT_LIST_POINTER> myArray; should be OK too.

NPE · Accepted Answer · 2012-02-29 08:55:53Z

2

You allocate an array of size p:

INT_LIST_POINTER myArray = new INT_LIST[p];

and then proceed to initialize n elements:

for (int i=0; i<n; i++){

Unless p and n are the same thing, this doesn't look right.

P.S. Don't forget to delete[] myArray when you're done with it.

answered Feb 29, 2012 at 8:55

NPE

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2 Comments

Will Ness Over a year ago

more importantly this allocates a fixed sized array yet again.

Carl Davis Over a year ago

You are also correct, I have changed the wording in the original post, I do not need it to be fully dynamic.

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