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C++ Function Return Array

General and Gameplay Programming Programming

Started by SulphurTenM November 23, 2007 08:41 AM

9 comments, last by SulphurTenM 16 years, 4 months ago

SulphurTenM

122

Author

November 23, 2007 08:41 AM

I know this seems REALLY stupid, but I want to make a function return an array, a 2-dimensional array. Now, I know this can be done really easy in Java: -


public int [][] getArr()
{
   int [][] newArr = new int[4][2] ;

   return( newArr ) ;
}

But it's a little more complex than this... The array I want returned is part of a class. Example: -


//header file
#ifndef HEADER_FILE
#define HEADER_FILE

class HeaderFile
{
private:
int arr[4][2] ;
public:
HeaderFile() ;
int [][] getArr() ; //this is wrong
} ;

#endif


//implementation file
#include "HeaderFile.h"

HeaderFile::HeaderFile()
{
for( int i = 0 ; i < 4 ; i++ )
{
arr[0] = i ;
arr[1] = i+1 ;
}
}

int [][] HeaderFile::getArr() //this is wrong
{
return( arr ) ;
}

Somewhere in another class or the main file: -


//...
HeaderFile hf = HeaderFile() ;

int arr[4][2] ;

arr = hf.getArr() ; //this is the way I want it
//...

How do I do this? I don't want to have to use vectors or anything like that... Templates and pointers also.... why can this not be as simple as in Java? (Don't answer that) How do I get the desired result? I am using slightly wrong syntax? Or do I have to completely rewrite some parts?

GLUT Setup: -Dev C++ 4.9.9.2GPU: GeForce 7600GT (256mb)CPU: Core 2 Due 1.86RAM: 1Gig

rvdwerf

102

November 23, 2007 09:14 AM

I'am sry to tell you but a function cannot return an array.
You need to return a pointer to an array instead.

SulphurTenM

122

Author

November 23, 2007 09:16 AM

Urg. Ok then....
I will figure out a long winded way....

I feared this would be the case... thanks anyway...

GLUT Setup: -Dev C++ 4.9.9.2GPU: GeForce 7600GT (256mb)CPU: Core 2 Due 1.86RAM: 1Gig

Nitage

1,107

November 23, 2007 09:23 AM

You'd probably be better of returning a reference to a std::vector.

rip-off

11,000

November 23, 2007 09:38 AM

Often, get...() functions indicate poor design where object behaviour is embedded in client classes. Ask yourself: why am I returning this array? What does the array represent?

If your class is a POD type, then why not have the member public?
You could embed the array in a structure and return a const reference to that structure:

struct InnerArray {    int arr[4][2]};class HeaderFile{private:   InnerArray inner;public:    HeaderFile() ;    const InnerArray &getArr();};

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Antheus

2,410

November 23, 2007 09:54 AM

Quote:Now, I know this can be done really easy in Java: -

C++ equivalent of that would be:

typedef std::vector< std::vector<int> > MyArray;class Header {MyArray &getArr() {  return arr;}private:  MyArray arr;}

The arrays in Java take care of all the allocations and bounds checking - they are equivalent to std::vector, not raw arrays or pointers.

The other way is to use the struct wrapper as mentioned above. But by using arrays in such liberal manner, you're setting yourself up for problems down the line.

Quote:How do I do this? I don't want to have to use vectors or anything like that...
Templates and pointers also.... why can this not be as simple as in Java? (Don't answer that)

But I have to, since it's the cause of your problem.

If you want Java functionality, use vectors.

BTW: what does your array represent?

Nuno1

161

November 23, 2007 10:12 AM

It is possible to pass the array through an object, but it seems like you are doing somthing wrong.

Why not provide a function like Get/PutArrayItem( int row, int col ) that will provide an access to the array inside your object ?

Nuno1

Zahlman

1,682

November 23, 2007 10:22 AM

Why are you exposing this data directly to the outside world? This is coming from someone with a Java background?! What does the data represent exactly?

For that matter, why would you have a default constructor for something that evidently (from the name) needs to be read from a file?

SulphurTenM

122

Author

November 23, 2007 06:53 PM

The examples I used were purely examples, the names were descriptive of what they are, not what they model...

I have "solved" it by making my own Array object and passing that around... with the suggested accessor and mutator methods....

I know it's not the perfect way... but thanks for all of your ideas.

I guess I should have realised that Java takes care of all the "messy" stuff...

I am making tetris in C++ with OpenGL/GLUT. The array contains the locations of each of the blocks of a piece.

While I am sure there are some much more efficient ways of coding this, I am doing it an OOD/OOP way. I am not going to claim that I am doing in a completely correct way. However, I have so far got all seven shapes falling down the screen and a given rate, you can "hard drop" a shape, and you can move it left and right until it hits the sides.

I have yet to get the following working: -
Rotation
Collision (everything from hitting the bottom to hitting other pieces to line completion)
Scoring
Display of next shape

However, I see little difficulty in completing these. I guess this is for a different forum....

I am doing this to prove to myself that I can.
I have made previous game-like OpenGL programs, but they are not complete.
Example of such a program.

[Edited by - SulphurTenM on November 23, 2007 7:53:25 PM]

GLUT Setup: -Dev C++ 4.9.9.2GPU: GeForce 7600GT (256mb)CPU: Core 2 Due 1.86RAM: 1Gig

Dancin_Fool

785

November 23, 2007 07:01 PM

Quote:Original post by SulphurTenM
I guess I should have realised that something like this is beyond C++...

LOL!!! As you've been shown earlier, it's quite possible in c++ through std::vector. If you'll use an array in java, why wouldn't you use c++'s vector class?

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