This documentation is archived and is not being maintained.

Marshal.AllocCoTaskMem Method

Allocates a block of memory of specified size from the COM task memory allocator.

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

[SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]
public static IntPtr AllocCoTaskMem(
	int cb


Type: System.Int32

The size of the block of memory to be allocated.

Return Value

Type: System.IntPtr
An integer representing the address of the block of memory allocated. This memory must be released with Marshal.FreeCoTaskMem.


There is insufficient memory to satisfy the request.

AllocCoTaskMem is one of two memory allocation API methods in the Marshal class. (Marshal.AllocHGlobal is the other.) The initial memory content returned is undefined, and the allocated memory can be larger than the requested number of bytes. This method exposes the CoTaskMemAlloc COM API method, which is referred to as the COM task memory allocator. For additional information about CoTaskMemAlloc, see the MSDN Library.


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.

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, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

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, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0