How to use variables declared within an if statement?

Question

Last time I had a similar question, but we figured out if initialize and set a value for the variable before the logic statement then I can use the value that was generated within the logic statement.

This time, I want to call one of two method overloads depending on if the connection string is empty or not. Like so.

if (ConnectionString != "") // if there is something in the config file work with it
{
  SqlConnection dataConnection = new SqlConnection(ConnectionString);
}
else
{
  SqlConnection dataConnection = new SqlConnection();
}

try {
  // ...

The problem is that anything in the try block fails because it does not know about the dataConnection.

How can do I do this in a way to make it work?

If you don't have a connection string where do you expect it to come from? Don't think that SqlConnection will invent it or that it will fall from the sky. What do you do in the else condition? Crash? — Darin Dimitrov
– Darin Dimitrov, Commented Jul 17, 2011 at 13:31
Thanks everyone for the wonderful answers! Very much clearer now. — Rob
– Rob, Commented Jul 17, 2011 at 21:25

CD.. · Accepted Answer · 2011-07-17 13:50:21Z

5

You can do it like this:

SqlConnection dataConnection = !string.IsNullOrEmpty(ConnectionString)
    ? new SqlConnection(ConnectionString) :  new SqlConnection();

Or:

SqlConnection dataConnection;
if (string.IsNullOrEmpty(ConnectionString))
{
    dataConnection = new SqlConnection(ConnectionString);
}
else
{
    dataConnection = new SqlConnection();
}

edited Jul 17, 2011 at 13:50

answered Jul 17, 2011 at 13:30

CD..

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Comments

Marc Gravell · Accepted Answer · 2011-07-17 13:35:45Z

3

Declare it (uninitialized) outside:

SqlConnection conn;
if(string.IsNullOrEmpty(connectionString)) {
    conn = new SqlConnection();
} else {
    conn = new SqlConnection(connectionString);
}

If the logic is simple, a conditional is possible too:

SqlConnection conn = string.IsNullOrEmpty(connectionString)
     ? new SqlConnection() : new SqlConnection(connectionString);

The latter is much easier to use with a using block, as it can be done inline.

edited Jul 17, 2011 at 13:35

answered Jul 17, 2011 at 13:30

Marc Gravell

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Comments

LarsTech · Accepted Answer · 2011-07-17 13:30:54Z

1

You have to have the variable outside the if block:

SqlConnection dataConnection;
if (ConnectionString != "") // if there is something in the config file work with it
{
  dataConnection = new SqlConnection(ConnectionString);
}
else
{
  dataConnection = new SqlConnection();
}

answered Jul 17, 2011 at 13:30

LarsTech

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Comments

om-nom-nom · Accepted Answer · 2011-07-17 13:31:48Z

1

I think you should define connection before if statements

 SqlConnection dataConnection = null;
    if (ConnectionString != "") // if there is something in the config file work with it
        {
            dataConnection = new SqlConnection(ConnectionString);
        }
        else
        {
            dataConnection = new SqlConnection();
        }
        try
        {

answered Jul 17, 2011 at 13:31

om-nom-nom

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Comments

Muhammad Al-Own · Accepted Answer · 2011-07-17 13:33:24Z

1

You can declare the variable with null value out side the if statment and then use it inside the if statment and when you need to use it check if it's not null

SqlConnection dataConnection = null;
if (ConnectionString != "") // if there is something in the config file work with it
{
    dataConnection = new SqlConnection(ConnectionString);
}
else
{
    dataConnection = new SqlConnection();
}
try
{
    if(dataConnection != null)
        DoWhatYouWant();
}

answered Jul 17, 2011 at 13:33

Muhammad Al-Own

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