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Returning A 2D Array

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Started by Protocol_0 July 27, 2005 04:41 AM

6 comments, last by Protocol_0 18 years, 9 months ago

Protocol_0

100

Author

July 27, 2005 04:41 AM

I am having problems returning a 2D array. Can anybody supply me with any help? The data type is bool. I thought that I would just do it like this:


bool *testFunc();
{
	bool test[10][10]={true, true, true, true, true, true, true, true, true, true,
                         true, false, false, false, false, false, false, false, false, true,
				         true, false, false, false, false, false, false, false, false, true,
                         true, false, false, false, false, false, false, false, false, true,
                         true, false, false, false, false, false, false, false, false, true,
                         true, false, false, false, false, false, false, false, false, true,
                         true, false, false, false, false, false, false, false, false, true,
                         true, false, false, false, false, false, false, false, false, true,
                         true, false, false, false, false, false, false, false, false, true,
                         true, true, true, true, true, true, true, true, true, true};


	return test;
}

But that doesn't work. I have been trying for hours but can't get it right. I'm going to take a guess, but is this how 2d arrays work? If this is [10][10]?


                                         Memory Address
                            0x1 0x2 0x3 0x4 0x5 0x6 0x7 0x8 0x9 0xF            

0x00000001  pointer to ->   [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]       
0x00000002  pointer to ->   [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
0x00000003  pointer to ->   [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
0x00000004  pointer to ->   [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
0x00000005  pointer to ->   [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
0x00000006  pointer to ->   [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
0x00000007  pointer to ->   [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
0x00000008  pointer to ->   [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
0x00000009  pointer to ->   [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]
0x0000000F  pointer to ->   [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ]

"Hard work pays off for the future; laziness pays off now"

HAM

176

July 27, 2005 04:45 AM

test will fall out of scope in your example, so you wouldn't want to return it.

You'd need to dynamically create it with 'new.'

but if you are returning a pointer to an array you might want to return the dimensions as well.

in that case you could possibly either consider returning the information through the parameters (in/out) or returning a struct.

Returning through the parameters would be better in this case, as you woudln't want to call the function with out acquiring the pointer.

Example.

a function like so:
int * Myfunc();

could be called like

Myfunc();

and nothing is grabbing the pointer which would result in memory leak.

Protocol_0

100

Author

July 27, 2005 05:58 AM

Hmm, I'm not sure I quite understand. How would I use "new" to dynamically create a 2D array? I know how to create a 1D, but not 2D.

"Hard work pays off for the future; laziness pays off now"

rip-off

11,000

July 27, 2005 06:26 AM

if you make the array static like this:

[source lang = "cpp]bool **testFunc();{	static bool test[10][10]={ ... };	return test;}

also you have to return a pointer to a pointer

or new

[source lang = "cpp]bool **testFunc();{        const int SIZE = 10;	bool *test = new bool*[SIZE ];        for( int i = 0 ; i < SIZE  ; ++i )            test = new bool[ SIZE ];        // fill with data	return test;}

this is ugly and you have to release the pointers using delete[]

the methid you use really depends on what you are doing with the data

blog | twitter

BornToCode

1,185

July 27, 2005 06:50 AM

//Heere is an Example

bool Array[2][2];
for(int j=0;j<2;j++)
for(int k=0;k<2;k++)
Array[j[k]=false;
bool **GetArray=Array;
for(int j=0;j<2;j++)
for(int k=0;k<2;k++)
cout<<GetArray[j][k]<<endl;

Or
bool Array[2][2];
for(int j=0;j<2;j++)
for(int k=0;k<2;k++)
Array[j[k]=false;
bool **GetArray=new bool*[2];
for(int t=0;t<2;t++)
GetArray[t]=new bool[2];
for(int j=0;j<2;j++)
for(int k=0;k<2;k++)
GetArray[j][k]=Array[j][k];
for(int t=0;t<2;t++)
delete[] GetArray[t];
delete[] GetArray;

PS i did not test it but it is something like that hope that helps.

Protocol_0

100

Author

July 27, 2005 07:18 AM

Yaaay. I figured out another way to neatly load my 2D arrays. Thanks you all for your valued input.

rip-off: That's a good idea for your first example too. That's what I would have done if I didn't think of my new way of loading it.

In my class, the .h, I just simple defined the 2D bool array as static, and defined it through the .cpp file.

e.g

class maps  {public:	maps();	static bool    map1[10][10];	virtual ~maps();}; bool maps::map1[10][10]={true, true, true, true, true, true, true, true, true, true,                         true, false, false, false, false, false, false, false, false, true,				         true, false, false, false, false, false, false, false, false, true,                         true, false, false, false, false, false, false, false, false, true,                         true, false, false, false, false, false, false, false, false, true,                         true, false, false, false, false, false, false, false, false, true,                         true, false, false, false, false, false, false, false, false, true,                         true, false, false, false, false, false, false, false, false, true,                         true, false, false, false, false, false, false, false, false, true,                         true, true, true, true, true, true, true, true, true, true};

Thanks again.

"Hard work pays off for the future; laziness pays off now"

jimywang

100

July 27, 2005 07:36 AM

Probably not a direct answer to your question, but instead of creating a explicit 2d array, you can create a 1d array and use it as 2d. so you will have something like this

bool *test = new test [width*height];

and you can acesse a item by caculating the offset. Such an array can be return just as a pointer.

Protocol_0

100

Author

July 27, 2005 08:04 AM

Yeah, I actually thought of doing something like that. But I'm the type of person who likes my code to look fancy. I have never used 2D arrays before, so I thought that it would be a good time to learn for the type of game I'm making.

"Hard work pays off for the future; laziness pays off now"

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