Testing object pointer for null

Hello,

I have created several objects for my program:

State
County
Municipality
Data Layer

The objects are setup as follows:

The State object has an array of Countie pointers
The County object has an array of Municipalities pointers
The Municipality object has an array of Data Layers pointers

In other words:

<State> has 1 to many <Counties> has one to many <Municipalities> has 1 to many <Data Layers>.

In my program I search a directory structure recursively. The first directory is assigned as a county if the first county element of the State object is null.

However, I seem to have a tough time testing the county arrary for nulls.

I use a function entitled getCurCounty to return a pointer to the current county pointer of the State object in the following fashion:

Code:

//if the county pointer is null
			if(StateArg->getCurCounty() == 0)
			{
				cout << "About to create a county." << endl << endl; 
				getch();

				//add a county to the state object
				StateArg->addCounty(new County(fileStruct.name));
			
			}	//end if countyPtr is null

The getCurCounty() function's code is below:

Code:

County * State::getCurCounty()
{
	return counties[numOfCounties];

}	//end State::getCounty

How do I properly test the county arrary of pointers in my state object for nulls? The execution seems to bypass the if statement in the first code segment.

Have you tried replacing the line

Code:

if(StateArg->getCurCounty() == 0)

with:

Code:

if(StateArg->getCurCounty() == NULL)

I *think* (but don't quote me) that some compiliers distinguish between NULL and 0

fletch

> return counties[numOfCounties];

If you did
County *counties = new County[numOfCounties];
Then
1. If you didn't fill it with NULLs to start with, then it won't return NULL here
2. counties[numOfCounties] is actually outside the array


> some compiliers distinguish between NULL and 0
If you've got a pointer in part of the expression, then 0 and NULL should be the same thing in any decent compiler

Originally posted by Salem

If you did
County *counties = new County[numOfCounties];
Then
1. If you didn't fill it with NULLs to start with, then it won't return NULL here

That was the exact problem. I fixed it just yesterday. Thanks. I didn't realize you need to initialize the array of object pointers to null.

Do you always need to intialize arrays in this fashion?

> Do you always need to intialize arrays in this fashion?
The only arrays which are initialised by default are true arrays which are either global or static

Arrays which are local to a function, and everything you get from new (or malloc in C), initially contain garbage, and should be initialised by you.