. Operator (C# Reference)
The dot operator (.) is used for member access. The dot operator specifies a member of a type or namespace. For example, the dot operator is used to access specific methods within the .NET Framework class libraries:
// The class Console in namespace System:
System.Console.WriteLine("hello");
For example, consider the following class:
class Simple
{
public int a;
public void b()
{
}
}
Simple s = new Simple();
The variable s has two members, a and b; to access them, use the dot operator:
s.a = 6; // assign to field a;
s.b(); // invoke member function b;
The dot is also used to form qualified names, which are names that specify the namespace or interface, for example, to which they belong.
// The class Console in namespace System:
System.Console.WriteLine("hello");
The using directive makes some name qualification optional:
namespace ExampleNS
{
using System;
class C
{
void M()
{
System.Console.WriteLine("hello");
Console.WriteLine("hello"); // Same as previous line.
}
}
}
But when an identifier is ambiguous, it must be qualified:
namespace Example2
{
class Console
{
public static void WriteLine(string s){}
}
}
namespace Example1
{
using System;
using Example2;
class C
{
void M()
{
// Console.WriteLine("hello"); // Compiler error. Ambiguous reference.
System.Console.WriteLine("hello"); //OK
Example2.Console.WriteLine("hello"); //OK
}
}
}
C# Language Specification
For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.