Using Arraylist with arrays

[Vaden95]

I am trying to uae ArrayList to store arrays of structures, but I can't get my
data back after storing the arrays.
My (highly shrunk and modified) code is below. The problem is at the line
labled Line 1. I get an exception thrown saying:
"An unhandled exception of type 'System.InvalidCastException' occurred in
SLAP.exe
Additional information: Specified cast is not valid."

I have a watch at line 1 for al, and before the line is run, al is correctly
populated and shows the list of arrays of type A.

What is the problem, and how do you fix it. Any help would be most helpful.
By the way, I am new to VisualC++.NET, and I am trying to learn it by redoing
program that I have written in VC++.

Chuck Gantz


First, I have a structure

__gc struct A
{
public:
double a, b;
A(double ain, double bin)
: a(ain), b(bin){};
};

Then I have my main class that has an ArrayList
__gc class B
{
private:
//Only allow one copy of al to exist
static ArrayList* al;
public:
B()
{
al= new ArrayList();
ReadData();
A* llp = __try_cast<A*>(al->Item[2]); //Line 1- gives Exception
}

void ReadData()
{

 

[Rajeev Goel]

Hi Chuck,

Since each item in your ArrayList is itself an array, when you grab a
single item out of the ArrayList, you need to cast it to an array type.
The following worked for me:

A* llp[] = __try_cast<A*[]>(al->Item[2]);

Also, thanks for reducing the code down to the simplest repro case ... that
made it easy to find the problem. I don't know how "real" the code is that
you posted, but I did find a couple other errors that I wanted to bring to
your attention:

1.) Your "count" variable needs to be initialized to zero just before the
"do...while" loop, otherwise "count" keeps getting bigger and bigger and
you walk off the end of the "ar" array.

2.) The "do...while" loop has an off-by-one error. The "while" condition
should be "while (count < 5)" in order to correctly fill up all five
elements of the "ar" array.

Hope this helps.

--Rajeev
Visual Studio .NET
Microsoft Corp.

This posting is provided "AS IS" with no warranties, and confers no rights.

 

[Chuck Gantz]

Hi Rajeev,

Thanks for the fast reply. I put in the square brackets and everything
worked fine then.

Also, in the actual code, the errors you found are not present. The
program reads a file, and "count" is found in the file to determine the
size of the arrays.

Chuck Gantz