ZeroFreeCoTaskMemAnsi Method
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Marshal.ZeroFreeCoTaskMemAnsi Method (IntPtr)

 

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

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

[SecurityCriticalAttribute]
public static void ZeroFreeCoTaskMemAnsi(
	IntPtr s
)

Parameters

s
Type: System.IntPtr

The address of the unmanaged string to free.

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

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

using System;
using System.Runtime.InteropServices;
using System.Security;

class MarshalExample
{
     static void Main()
     {
         IntPtr unmanagedRef = IntPtr.Zero;

          // 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.SecureStringToCoTaskMemAnsi(passWord);

          if (unmanagedRef != IntPtr.Zero)
          {
              Console.WriteLine("Zeroing out unmanaged memory...");

              Marshal.ZeroFreeCoTaskMemAnsi(unmanagedRef);
          }
          passWord.Dispose();

         Console.WriteLine("Done.");
     }

     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;
     }
}

SecurityCriticalAttribute

requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1
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