Export (0) Print
Expand All
Expand Minimize

Marshal.ZeroFreeGlobalAllocAnsi Method

Frees an unmanaged string pointer that was allocated using the SecureStringToGlobalAllocAnsi method.

Namespace:  System.Runtime.InteropServices
Assembly:  mscorlib (in mscorlib.dll)

[SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]
public static void ZeroFreeGlobalAllocAnsi(
	IntPtr s
)

Parameters

s
Type: System.IntPtr

The address of the unmanaged string to free.

The ZeroFreeGlobalAllocAnsi method first zeros out and then frees unmanaged memory that was allocated using the SecureStringToGlobalAllocAnsi method.

NoteNote:

This method uses SecurityAction.LinkDemand to prevent it from being called from untrusted code; only the immediate caller is required to have SecurityPermissionAttribute.UnmanagedCode permission. If your code can be called from partially trusted code, do not pass user input to Marshal class methods without validation. For important limitations on using the LinkDemand member, see Demand vs. LinkDemand.

The following code example uses the SecureStringToGlobalAllocAnsi method to marshal and decrypt the contents of a SecureString object to a block of unmanaged memory. It then uses the ZeroFreeGlobalAllocAnsi method to zero out and dispose the unmanaged block.

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Security;
using System.Security.Principal;
using System.Text;

namespace SecureStringExample
{

    class MarshalExample
    {


        static void Main(string[] args)
        {
            IntPtr unmanagedRef = IntPtr.Zero;

            try
            {
                // Ask the user for a password.
                Console.Write("Please enter your password:");

                SecureString passWord = GetPassword();

                Console.WriteLine("Copying and decrypting the string to unmanaged memory...");

                // Copy the Secure string to unmanaged memory (and decrypt it).
                unmanagedRef = Marshal.SecureStringToGlobalAllocAnsi(passWord);

            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
            finally
            {
                if (unmanagedRef != IntPtr.Zero)
                {
                    Console.WriteLine("Zeroing out unmanaged memory...");

                    Marshal.ZeroFreeGlobalAllocAnsi(unmanagedRef);
                }
            }

            Console.WriteLine("Done.");

            Console.ReadLine();


        }

        public static SecureString GetPassword()
        {
            SecureString password = new SecureString();

            // get the first character of the password
            ConsoleKeyInfo nextKey = Console.ReadKey(true);

            while (nextKey.Key != ConsoleKey.Enter)
            {
                if (nextKey.Key == ConsoleKey.Backspace)
                {
                    if (password.Length > 0)
                    {
                        password.RemoveAt(password.Length - 1);

                        // erase the last * as well
                        Console.Write(nextKey.KeyChar);
                        Console.Write(" ");
                        Console.Write(nextKey.KeyChar);
                    }
                }
                else
                {
                    password.AppendChar(nextKey.KeyChar);
                    Console.Write("*");
                }

                nextKey = Console.ReadKey(true);
            }

            Console.WriteLine();

            // lock the password down
            password.MakeReadOnly();
            return password;
        }
    }
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

Community Additions

ADD
Show:
© 2014 Microsoft