Description
This enumeration is used by the DllImportAttribute to indicate the required modifications to the System.String arguments of an imported function.
[Note: See the DllImportAttribute class overview for an example that uses the CharSet enumeration.]
Example
using System;
using System.Runtime.InteropServices;
/// <summary>
/// Sample demonstrating the use of the CharSet enumeration.
/// Use this enumeration to specify how strings should be marshalled to
/// unmanaged code for methods decorated with DllImportAttribute and types
/// decorated with StructLayoutAttribute.
/// </summary>
internal class CharSetSample
{
private static void Main()
{
OSVERSIONINFO ovi = new OSVERSIONINFO();
// Given that CharSet.Auto was used for OSVERSIONINFO, we can work out
// how strings are being marshalled by getting the unmanaged size of
// OSVERSIONINFO.
ovi.dwOSVersionInfoSize = (uint)Marshal.SizeOf(typeof(OSVERSIONINFO));
switch (ovi.dwOSVersionInfoSize)
{
case 148:
Console.WriteLine(
"OSVERSIONINFO strings will be marshalled as ANSI.");
break;
case 276:
Console.WriteLine(
"OSVERSIONINFO strings will be marshalled as Unicode.");
break;
default:
Console.WriteLine(
"Unknown marshalling for OSVERSIONINFO strings.");
break;
}
if (GetVersionEx(ref ovi))
{
Console.Write(
"Detected OS version: {0}.{1}.{2}",
ovi.dwMajorVersion, ovi.dwMinorVersion, ovi.dwBuildNumber);
if (ovi.szCSDVersion.Length > 0)
{
Console.Write(" ({0})", ovi.szCSDVersion);
}
Console.WriteLine();
}
else
{
Console.WriteLine("GetVersionEx failed.");
}
Console.WriteLine();
Console.WriteLine();
Console.WriteLine("Press Enter to continue");
Console.ReadLine();
}
// The OSVERSIONINFO type to use with GetVersionEx. Note that CharSet.Auto
// is used so the type of string marshalling used is based on the OS.
[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]
private struct OSVERSIONINFO
{
public uint dwOSVersionInfoSize;
public uint dwMajorVersion;
public uint dwMinorVersion;
public uint dwBuildNumber;
public uint dwPlatformId;
// Note that szCSDVersion is actually limited to SizeConst - 1 chars.
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=128)]
public string szCSDVersion;
}
// Win32 method to retrieve information about the OS. .NET code would
// typically use Environment.OSVersion, although it's worth noting that
// GetVersionEx can retrieve the service pack string as well. Note that
// CharSet.Auto is used so the type of string marshalling used is based on
// the OS (Unicode on WinNT family and ANSI on Win9x family).
[DllImport("kernel32.dll", CharSet=CharSet.Auto, SetLastError=true)]
private static extern bool GetVersionEx(
ref OSVERSIONINFO lpVersionInformation);
}
The output is
OSVERSIONINFO strings will be marshalled as Unicode.
Detected OS version: 5.1.2600 (Service Pack 2)
Press Enter to continue
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