C# Signature:

[DllImport("advapi32.dll")]
static extern IntPtr FreeSid(IntPtr pSid);
- or -
[DllImport("advapi32")]
public static extern void FreeSid(IntPtr pSid);
(since FreeSid returns a PVOID)

VB Signature:

Declare Function FreeSid Lib "advapi32.dll" (ByVal pSid As IntPtr) As IntPtr

User-Defined Types:

None.

Notes:

None.

Tips & Tricks:

Please add some!

Sample Code:

using System;

using System.Runtime.InteropServices;

using System.Text;

class Test

{

  static void Main()  {
    string strSid = GetSIDForAccount("Administrator");
    Console.WriteLine( strSid  );
  }

  public static string GetSIDForAccount(string Account) {
    long winErrorCode = 0; //contains the last error

    //pointer and size for the SID
    IntPtr pSid = IntPtr.Zero;
    int iSidSize = 0;
    //StringBuilder for Domain
    StringBuilder sbDomain = new StringBuilder();
    int iDomainSize = 0;

    //account-type variable for lookup
    int iAccountType = 0;

    //get required buffer size  (iSidSize=0 causes this...)
    LookupAccountName(String.Empty, Account, pSid, ref iSidSize,
      sbDomain, ref iDomainSize, ref iAccountType);

    //allocate buffers
    sbDomain = new StringBuilder(iDomainSize);
    pSid = Marshal.AllocHGlobal(iSidSize);

    //lookup the SID for the account
    bool bResult = LookupAccountName(String.Empty,
                     Account,
                     pSid,
                     ref iSidSize,
                     sbDomain,
                     ref iDomainSize,
                     ref iAccountType);
    if (!bResult) {
      winErrorCode = GetLastError();
      Console.WriteLine("LookupAccountName failed: "+ winErrorCode);
      FreeSid(pSid);
      throw new ApplicationException("Could not read SID");
    }

    string strSID = "";
    if ( ConvertSidToStringSid( pSid, ref strSID)) {
      FreeSid(pSid);
      return strSID;
    } else {
      throw new ApplicationException("Could not convert SID");
    }
  }

  [DllImport("kernel32.dll")]
  private static extern int GetLastError();

  [DllImport( "advapi32.dll", CharSet=CharSet.Auto, SetLastError=true, PreserveSig=true)]
  private static extern bool LookupAccountName(
    string lpSystemName,
    string lpAccountName,
    IntPtr psid,
    ref int cbsid,
    StringBuilder domainName,    //StringBuilder or string?
    ref int cbdomainLength,
    ref int use );

  [DllImport("advapi32.dll", CharSet=CharSet.Auto)]
  private static extern bool ConvertSidToStringSid(
    IntPtr pSID,
    [In,Out,MarshalAs(UnmanagedType.LPTStr)] ref string strSID);

  [DllImport("advapi32")]
  private static extern void FreeSid(IntPtr pSid);  

}

Alternative Managed API:

Do you know one? Please contribute it!