Marshaling Common Types
The CLR
marshaler is a .NET facility that knows about the core types used by COM and
the Windows API, and provides default translations to CLR types for you. The bool
type, for instance, can be translated into a two-byte Windows BOOL type or
a four-byte Boolean type. Using the MarshalAs
attribute, you can override a default translation:
using System.Runtime.InteropServices; static extern int Foo([MarshalAs(UnmanagedType.LPStr)] string s);
In this case, the marshaler was told to use LPStr, so it will always
use ANSI characters. Array classes and the StringBuilder
class copy the
marshaled value from an external function back to the managed value, as follows:
using System; using System.Text; using System.Runtime.InteropServices; class Test { [DllImport("kernel32.dll")] static extern int GetWindowsDirectory(StringBuilder sb, int maxChars); static void Main() { StringBuilder s = new StringBuilder(256); GetWindowsDirectory(s, 256); Console.WriteLine(s); } }
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