Ad:

C++ Discussion Thread
Marked Solved
Views: 865

Page 1
2
Next

You are currently viewing page 1 of this multi-page discussion thread

Permalink

Jul 2nd, 2009

C++ arrays

Expand Post »

Please tell me how to create a multi diminsional array using pointer(dynamic array, set size at run time).

Similar Threads

(reformatted) How to return Multi-Dimensional Arrays in C++
What relation does **indirection operator have with Multidimensional Arrays in C++
Arrays in C++
How to Return Multidimensional Arrays in C++
C file input/output 2D arrays. in C

thilinam

Reputation Points: 10

Solved Threads: 0

Light Poster

Offline

35 posts
since Sep 2008

Permalink

Jul 2nd, 2009

Re: C++ arrays

Declare pointer to pointer variable,

C++ Syntax (Toggle Plain Text)

     int **ptr;

How many one dim arrays?

C++ Syntax (Toggle Plain Text)
 p=new int*[4];
 p=new int*[4];

What is the size of each one array?

C++ Syntax (Toggle Plain Text)
 *(p+0)=new int[3];
 *(p+1)=new int[3];
 *(p+2)=new int[3];
 *(p+3)=new int[3];
 *(p+0)=new int[3];
 *(p+1)=new int[3];
 *(p+2)=new int[3];
 *(p+3)=new int[3];

How to freed allocated memory?

C++ Syntax (Toggle Plain Text)
delete []p;
delete []p;

adatapost

Moderator

Reputation Points: 2136

Solved Threads: 1228

Posting Genius

Offline

6,527 posts
since Oct 2008

Permalink

Jul 2nd, 2009

Re: C++ arrays

I'd recommend a container class where you pass two axis but gets resolved to a single array allocation.

This is only one example of how to solve this!

C++ Syntax (Toggle Plain Text)
class IntArray
{
private:
	int *pInt;
	unsigned int nWidth;
	unsigned int nHeight;
 
public:
	IntArray( unsigned int w, unsigned int h );
	~IntArray();
	void Set( unsigned int x, unsigned int y, int val );
	int Get( unsigned int x, unsigned int y );
};
 
void IntArray::IntArray( unsigned int w, unsigned int h )
{
	pInt = new int[ w * h ];
	nWidth = w;
	nHeight = h;
}
 
IntArray::~IntArray()
{
	if (NULL != pInt)
	{
		delete[] pInt;
	}
}
 
int IntArray::Get( unsigned int x, unsigned int y )
{
	return pInt[ y * nWidth + x  );
}
 
void IntArray::Set( unsigned int x, unsigned int y, int val )
{
	pInt[ y * nWidth + x ] = val;
}
class IntArray
{
private:
	int *pInt;
	unsigned int nWidth;
	unsigned int nHeight;

public:
	IntArray( unsigned int w, unsigned int h );
	~IntArray();
	void Set( unsigned int x, unsigned int y, int val );
	int Get( unsigned int x, unsigned int y );
};

void IntArray::IntArray( unsigned int w, unsigned int h )
{
	pInt = new int[ w * h ];
	nWidth = w;
	nHeight = h;
}

IntArray::~IntArray()
{
	if (NULL != pInt)
	{
		delete[] pInt;
	}
}

int IntArray::Get( unsigned int x, unsigned int y )
{
	return pInt[ y * nWidth + x  );
}

void IntArray::Set( unsigned int x, unsigned int y, int val )
{
	pInt[ y * nWidth + x ] = val;
}

wildgoose

Reputation Points: 546

Solved Threads: 99

Practically a Posting Shark

Offline

891 posts
since Jun 2009

Permalink

Jul 2nd, 2009

Re: C++ arrays

Click to Expand / Collapse Quote originally posted by adatapost ...

How to freed allocated memory?
C++ Syntax (Toggle Plain Text)
delete []p;
delete []p;

Don't you also have to delete each p array?

If you aren't sure, the answer is yes, delete each array first before deleting p itself.

Last edited by WaltP; Jul 2nd, 2009 at 3:15 am.

WaltP

Moderator

Reputation Points: 3278

Solved Threads: 890

Posting Sage

Offline

7,718 posts
since May 2006

Permalink

Jul 2nd, 2009

Re: C++ arrays

Each new[] array requires a delete.
So in that other variation, each branch leg has to be deleted first then the backbone.

wildgoose

Reputation Points: 546

Solved Threads: 99

Practically a Posting Shark

Offline

891 posts
since Jun 2009

Permalink

Jul 2nd, 2009

Re: C++ arrays

wildgooe and WaltP,
Thanks for correction.

delete has two forms:
1. delete pointer - deallocates a single element
2. delete []pointer - deallocates arrays of elements.

adatapost

Moderator

Reputation Points: 2136

Solved Threads: 1228

Posting Genius

Offline

6,527 posts
since Oct 2008

Permalink

Jul 2nd, 2009

Re: C++ arrays

You could use std::vector's of std::vector's - then you don't have to worry about new() and delete().

daviddoria

Featured Poster

Reputation Points: 437

Solved Threads: 204

Posting Virtuoso

Offline

1,968 posts
since Feb 2008

Permalink

Jul 2nd, 2009

Re: C++ arrays

I would recommend:

C++ Syntax (Toggle Plain Text)
int **array;
int sizeX,sizeY;
sizeX = 5; // set to whatever
sizeY = 5; // set to whatever
array = new int*[sizeY];
for(int i = 0; i < sizeY; i++)
    array[i] = new int[sizeX];
 
// Then to delete:
for(int i = 0; i < sizeY; i++)
    delete array[i];
delete [] array; // i think you need the [] here but not sure.
int **array;
int sizeX,sizeY;
sizeX = 5; // set to whatever
sizeY = 5; // set to whatever
array = new int*[sizeY];
for(int i = 0; i < sizeY; i++)
    array[i] = new int[sizeX];

// Then to delete:
for(int i = 0; i < sizeY; i++)
    delete array[i];
delete [] array; // i think you need the [] here but not sure.

---------------------
This is what i used in something i made, but remade it here in 5 mins. No guarantee it works -.- Even though it should...

Last edited by u8sand; Jul 2nd, 2009 at 10:02 am.

u8sand

Reputation Points: 78

Solved Threads: 15

Junior Poster

Offline

131 posts
since Dec 2008

Permalink

Jul 2nd, 2009

Re: C++ arrays

line 11 of that code snippet is wrong. It should be delete[], not delete.

Ancient Dragon

Sponsor

Team Colleague

Featured Poster

Reputation Points: 5608

Solved Threads: 2282

Retired and Enjoying Life

Online

21,950 posts
since Aug 2005

Permalink

Jul 2nd, 2009

Re: C++ arrays

O Sorry, it don't let me edit now -.-
Here:

C++ Syntax (Toggle Plain Text)
int **array;
int sizeX,sizeY;
sizeX = 5; // set to whatever
sizeY = 5; // set to whatever
array = new int*[sizeY];
for(int i = 0; i < sizeY; i++)
    array[i] = new int[sizeX];
 
// Then to delete:
for(int i = 0; i < sizeY; i++)
    delete [] array[i];
delete [] array;
int **array;
int sizeX,sizeY;
sizeX = 5; // set to whatever
sizeY = 5; // set to whatever
array = new int*[sizeY];
for(int i = 0; i < sizeY; i++)
    array[i] = new int[sizeX];
 
// Then to delete:
for(int i = 0; i < sizeY; i++)
    delete [] array[i];
delete [] array;

Last edited by u8sand; Jul 2nd, 2009 at 10:43 am.

u8sand

Reputation Points: 78

Solved Threads: 15

Junior Poster

Offline

131 posts
since Dec 2008

Page 1
2
Next

This thread is solved

Either the thread starter or a moderator has marked this thread as solved. You can most likely trust the responses and answers given. There is most likely no reason for any further responses to be posted here. If you have a related question, please start a new thread in this forum instead.

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

Previous Thread in C++ Forum Timeline: I'm confused

Next Thread in C++ Forum Timeline: slowly but surely

DaniWeb Message

Cancel Changes

User Name
Password