Array problem

[mituozo]

Hello everyone,

I'm trying to make an array from the return of a MySQL query but keep getting the following error message:

Error 1 Use of unassigned local variable 'QueryArray'

The line it refers to is the "return QueryArray;"

I keep trying different methods to try and get this to work but I'm getting no where.. So any help would be much appreciated. It's a generic query handler I'm making, so I don't know how big the array is going to be before the query is executed..


public static string[][] ReturnQueryArray(MySql.Data.MySqlClient.MySqlConnection Source, string SQLQuery)
{
MySql.Data.MySqlClient.MySqlCommand MyQuery = Source.CreateCommand();
MySql.Data.MySqlClient.MySqlDataReader Reader;
MyQuery.CommandText = SQLQuery;
Reader = MyQuery.ExecuteReader();

int counter = 0;
string[][] QueryArray;

while (Reader.Read())
{
for (int i = 0; i < Reader.FieldCount; i++)
{
QueryArray[counter][i] = Reader.GetValue(i).ToString();

}

counter = counter + 1;
}
return QueryArray;
}

[TheCPUWizard]

Where are you ACTUALLY inisitalizing this:

string[][] QueryArray;


hint: The compiler is correctly telling you that you have NOT!

[mituozo]

I thought that:


QueryArray[counter][i] = Reader.GetValue(i).ToString();


Would count as initialising it?

How can you initialise something prior to that when not knowing the length of either of the dimensions of the array?

[TheCPUWizard]

Arrays MUST be initialized by a direct or indirect call to new:


int [] a = new int[10];


Arrays MUST have a known size at time of initialization. Collection Classes do not. See List<T>

[mituozo]

Ah, is there a way of going about having an effectively multiple dimensional List then, much like an array ?

[BigEd781]

Sure, you could create a list of lists.

List<List<string>> multi_list = new List<List<string>>();

[mituozo]

Ah, thanks for your help.. Sorry for all the questions, one last one, but how would you then Add to the list/list of lists?

Wouldn't multi_lists.add() just add to the second list?

[BigEd781]

So, I think that you actually wanted to use

string[ , ]

instead of a jagged array. Using a List of Lists is actually pretty ugly, sorry. I am actually at work (!), so let me think about it. I would try to figure out the size that you need beforehand, but surely there are more experienced programmers around here that have a better answer for you.

[mituozo]

Right, I've got it to work okay, here's what I did if you're curious..


public static List<List<string>> ReturnQueryArray(MySql.Data.MySqlClient.MySqlConnection Source, string SQLQuery)
{
MySql.Data.MySqlClient.MySqlCommand MyQuery = Source.CreateCommand();
MySql.Data.MySqlClient.MySqlDataReader Reader;
MyQuery.CommandText = SQLQuery;
Reader = MyQuery.ExecuteReader();

int counter = 0;
List<List<string>> ResultList = new List<List<string>>();
while (Reader.Read())
{
List<string> ResultList2 = new List<string>();
for (int i = 0; i < Reader.FieldCount; i++)
{
ResultList2.Add(Reader.GetValue(i).ToString());

/* ResultList.Add(Reader.GetValue(i).ToString()); */

}
ResultList.Add(ResultList2);
counter = counter + 1;
}
return ResultList;
}

[BigEd781]

Yup, that's where I was going. Create a sub List and then add it to the parent.

[mituozo]

Yeah, there must be a better way but I guess this'll do for now.. Thanks for your help.