When a method declaration includes an extern modifier, the method is said to be an external method. External methods are implemented externally, typically using a language other than C#. Because an external method declaration provides no actual implementation, the method-body of an external method simply consists of a semicolon.

The mechanism by which linkage to an external method is achieved, is implementation-defined.

[Example: The following example demonstrates the use of the extern modifier in combination with a DllImport attribute that specifies the name of the external library in which the method is implemented:

using System.Text; using System.Security.Permissions; using System.Runtime.InteropServices; class Path { [DllImport("kernel32", SetLastError=true)] static extern bool CreateDirectory(string name, SecurityAttribute sa); [DllImport("kernel32", SetLastError=true)] static extern bool RemoveDirectory(string name); [DllImport("kernel32", SetLastError=true)] static extern int GetCurrentDirectory(int bufSize, StringBuilder buf); [DllImport("kernel32", SetLastError=true)] static extern bool SetCurrentDirectory(string name); }

end example]