Unreachable code detected

Question

I'm getting a "Unreachable code detected" message in Visual Studio at the point con.close() in my code below. Can you spot what I've done wrong?

private int chek1(String insert)
{
    OleDbConnection con = new OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=d:\\sdb.mdb");
    OleDbCommand com = new OleDbCommand("select count(*) from sn where sn='" + insert + "\'", con);           
    con.Open();

    int po = (int)com.ExecuteScalar();           
    if (po > 0)
        return 1;
    else
        return 0;
    con.Close();    
}

Answer 1

The function exits when you return 1 or 0 (when you return anything, but 1 or 0 in your case); so there's no way that con.Close() can be called.

In the code you've posted, you're guaranteed to return, since you have a return statement in both branches of your if-statement. If only one branch had a return statement, con.Close() could still be reached.

But you shouldn't be using Close that way anyway -- you should be using using statements.

using (OleDbConnection con = new OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=d:\\sdb.mdb"))
using (OleDbCommand com = new OleDbCommand("select count(*) from sn where sn='" + insert + "\'", con))
{
    con.Open();

    int po = (int)com.ExecuteScalar();           
    if (po > 0)
        return 1;
    else
        return 0;

    // con.Close and con.Dispose will be called automatically at the end of the using block
}      

Answer 2

You have an if / else above that will always trigger a return:

    if (po > 0)
        return 1;
    else
        return 0;

So there is no possible way any code will execute after this snippet of code.

Answer 3

 con.Close();

is unreachable. Either branch of the if statement returns so that line cannot be reached.

Answer 4

    if (po > 0)
        return 1;
    else
        return 0;

There's your problem. Either po > 0 is true, in which case 1 is returned, either it isn't, in which case 0 is returned. No matter what, con.Close(); will never get executed.

Answer 5

you have a return before the end of your routine. it will break out of that function before the Close() statement is called. just move con.Close() before your if block.

Answer 6

In addition to considering all the above answers, better consider using try..catch..finally and in finally, close the connection object. This will be better coding approach. You can improve your code like this.

private int chek1(String insert) {    
        OleDbConnection con = new OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=d:\\sdb.mdb");
        OleDbCommand com = new OleDbCommand("select count(*) from sn where sn='" + insert + "\'", con);       
    try{    
        con.Open();

        int po = (int)com.ExecuteScalar();           
        if (po > 0)
            return 1;
        else
            return 0;
    catch(Exception e){
    }finally{
        con.Close();
    }
}

Answer 7

This will work

int po = (int)com.ExecuteScalar();           
int result = 0;
if (po > 0) {
    result = 1;
}
con.Close();
return result;

in your case the con.Close(); is not reached because the function returns earlier

Answer 8

Change your code to

private int chek1(String insert)
{
    OleDbConnection con = null;
    try {
    con = new OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=d:\\sdb.mdb");
    OleDbCommand com = new OleDbCommand("select count(*) from sn where sn='" + insert + "\'", con);           
    con.Open();

    int po = (int)com.ExecuteScalar();           
    if (po > 0)
        return 1;
    else
        return 0;
    }
    finally {
        con.Close();
    }
}

Answer 9

The reason has been answered, you should look at using the using statement. It will close your connection for you automatically.

using (OleDbConnection con = new OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=d:\\sdb.mdb"))
{
    using (OleDbCommand com = new OleDbCommand("select count(*) from sn where sn='" + insert + "\'", con))
    {
        con.Open();
        int po = (int)com.ExecuteScalar();           
        if (po > 0)
            return 1;
        else
            return 0;
    }
}

Answer 10

Your code could be like this:

private int check(string sn)
{
    using (OleDbConnection connection = new OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=d:\\sdb.mdb"))
    using (OleDbCommand command = connection.CreateCommand())          
    {
        command.CommandText = "SELECT COUNT(*) FROM sn WHERE sn=?";
        command.Parameters.Add("@sn", sn));
        con.Open();               
        return ((int)com.ExecuteScalar() > 0) ? 1 : 0;
    }
}

Answer 11

It is unreachable because the method already return a value before its execute the con.Close() method.

Please Modify your code into:

using (OleDbConnection con = new OleDbConnection("provider=microsoft.jet.oledb.4.0;data source=d:\\sdb.mdb"))
{
    using (OleDbCommand com = new OleDbCommand("select count(*) from sn where sn='" + insert + "\'", con))
    {
        con.Open();

        int po = (int)com.ExecuteScalar();  

        return po > 0 ? 1 : 0;
    }
}