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C++ arrays

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Join Date: Sep 2008

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thilinam

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C++ arrays

Jul 2nd, 2009

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

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adatapost

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Re: C++ arrays

Jul 2nd, 2009

Declare pointer to pointer variable,

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     int **ptr;

How many one dim arrays?

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

What is the size of each one array?

 Help with Code Tags 
 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?

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

Failure is not fatal, but failure to change might be. - John Wooden

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wildgoose

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Re: C++ arrays

Jul 2nd, 2009

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!

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 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;
}

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WaltP

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Re: C++ arrays

Jul 2nd, 2009

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Originally Posted by adatapost

How to freed allocated memory?
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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.

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1) Never do today that which can be put off until tomorrow
2) Tomorrow never comes

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wildgoose

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Re: C++ arrays

Jul 2nd, 2009

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

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adatapost

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Re: C++ arrays

Jul 2nd, 2009

wildgooe and WaltP,
Thanks for correction.

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

Failure is not fatal, but failure to change might be. - John Wooden

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daviddoria daviddoria is offline

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Re: C++ arrays

Jul 2nd, 2009

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

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u8sand

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Re: C++ arrays

Jul 2nd, 2009

I would recommend:

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 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.

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Ancient Dragon Ancient Dragon is offline

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Re: C++ arrays

Jul 2nd, 2009

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

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u8sand

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Re: C++ arrays

#10

Jul 2nd, 2009

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

 Help with Code Tags 
 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;