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 Shared Sub ZeroFreeCoTaskMemAnsi (
	s As IntPtr
)

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.

Imports System.Runtime.InteropServices
Imports System.Security

Module Example
    Sub Main()
        Dim unmanagedRef As IntPtr

         ' Ask the user for a password.
         Console.Write("Please enter your password: ")
         Dim passWord As SecureString = 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.Size Then
             Console.WriteLine("Zeroing out unmanaged memory...")
             Marshal.ZeroFreeCoTaskMemAnsi(unmanagedRef)
         End If
         passWord.Dispose()

        Console.WriteLine("Done.")
    End Sub



    Function GetPassword() As SecureString
        Dim password As New SecureString()

        ' get the first character of the password
        Dim nextKey As ConsoleKeyInfo = Console.ReadKey(True)

        While nextKey.Key <> ConsoleKey.Enter
            If nextKey.Key = ConsoleKey.BackSpace Then
                If password.Length > 0 Then
                    password.RemoveAt(password.Length - 1)

                    ' erase the last * as well
                    Console.Write(nextKey.KeyChar)
                    Console.Write(" ")
                    Console.Write(nextKey.KeyChar)
                End If
            Else
                password.AppendChar(nextKey.KeyChar)
                Console.Write("*")
            End If

            nextKey = Console.ReadKey(True)
        End While

        Console.WriteLine()

        ' lock the password down
        password.MakeReadOnly()
        Return password

    End Function
End Module

SecurityCriticalAttribute

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

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1
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