Accessing windows registry in C#

Question

I am trying to get all the SQL Instances installed on a local machine with the help of following code:

RegistryKey rk = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\Microsoft SQL Server");
string[] instances = (string[])rk.GetValue("InstalledInstances");

if (instances.Length > 0)    //Error
{
    foreach (string instance in instances)
    {
        MessageBox.Show(instance);
    }
}

It is giving the following exception:

Object reference not set to an instance of an object.

I've manually checked the 'Registry-Editor' and the specified keys exist, also there are two SQL Instances on my system.

Now please tell me why it is not accessing the required key value?

Answer 1

I ran your code on my 64-bit machine. It worked fine. Make sure you platform is set to AnyCPU or x64 but not x86

Answer 2

This line could be the issue string[] instances = (string[])rk.GetValue("InstalledInstances");

Because RegistryKey.GetValue Method (String) returns a object and you are casting that in to string[]

before casting it to string[] you should check if the returned value is not null