What is the difference between the using statement and directive in C#?

Question

this is basically a tutorial question to ask since am a beginner I would like to what is a difference between the using statement we use at start of our C# code to include assembly and namespaces

like this:

using System.Web.Services;

and when we write inside the code within the method or code. like this:

using (SqlDataAdapter adapter = new SqlDataAdapter(cmd))

is there any difference or they both are same, any guidance would be helpful and appreciated.

Answer 1

The first (Using Directive) is to bring a namespace into scope.

This is for example, so you can write

StringBuilder MyStringBuilder = new StringBuilder();

rather than

System.Text.StringBuilder MyStringBuilder = new System.Text.StringBuilder();

---

The second (Using Statement) one is for correctly using (creating and disposing) an object implementing the IDisposable interface.

For example:

using (Font font1 = new Font("Arial", 10.0f)) 
{
    byte charset = font1.GdiCharSet;
}

Here, the Font type implements IDisposable because it uses unmanaged resources that need to be correctly disposed of when we are no-longer using the Font instance (font1).

Answer 2

using (SqlDataAdapter adapter = new SqlDataAdapter(cmd))

This using disposes the adapter object automatically once the control leaves the using block.

This is equivalent to the call

SqlDataAdapter adapter = new SqlDataAdapter(cmd)
adapter.dispose();

See official documentation on this: http://msdn.microsoft.com/en-us/library/yh598w02(v=vs.71).aspx