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GetLengthSid (advapi32)
Returns the length in bytes of a valid SID

C# Signature:

static extern uint GetLengthSid(IntPtr pSid);

VB Signature

    Public Declare Function GetLengthSid Lib "advapi32.dll"( _
        pSID As System.IntPtr _
    ) As Integer

User-Defined Types:



If pSid points to an unamanged array of bytes containing a SID, this function determines the length of the SID (by the formula: 8 + 4 times the value of the second byte), which you need to know, for example, when copying the SID into a managed byte array.

Consider also the use of CopySid instead of Marshal.Copy below. MSDN isn't clear if that is necessary or not, but better safe than sorry.

Tips & Tricks:

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Sample Code:

public static byte[] GetSidFromString(string stringSid)
    IntPtr pSid;
    if ( !ConvertStringSidToSid(stringSid, out pSid) )
        int length = (int) GetLengthSid(pSid);
        byte[] sid = new byte[length];
        Marshal.Copy(pSid, sid, 0, length);
        return sid;

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