Marshal.FreeHGlobal(IntPtr) Marshal.FreeHGlobal(IntPtr) Marshal.FreeHGlobal(IntPtr) Marshal.FreeHGlobal(IntPtr) Method

Definition

Frees memory previously allocated from the unmanaged memory of the process.

public:
 static void FreeHGlobal(IntPtr hglobal);
[System.Security.SecurityCritical]
public static void FreeHGlobal (IntPtr hglobal);
static member FreeHGlobal : nativeint -> unit
Public Shared Sub FreeHGlobal (hglobal As IntPtr)

Parameters

hglobal
IntPtr IntPtr IntPtr IntPtr

The handle returned by the original matching call to AllocHGlobal(IntPtr).

Examples

The following example demonstrates calling the FreeHGlobal method. This code example is part of a larger example provided for the Marshal class.

// Demonstrate how to call GlobalAlloc and 
// GlobalFree using the Marshal class.
IntPtr hglobal = Marshal::AllocHGlobal(100);
Marshal::FreeHGlobal(hglobal);
// Demonstrate how to call GlobalAlloc and 
// GlobalFree using the Marshal class.
IntPtr hglobal = Marshal.AllocHGlobal(100);
Marshal.FreeHGlobal(hglobal);
' Demonstrate how to call GlobalAlloc and 
' GlobalFree using the Marshal class.
Dim hglobal As IntPtr = Marshal.AllocHGlobal(100)
Marshal.FreeHGlobal(hglobal)

The following example demonstrates how to convert the contents of a managed String class to unmanaged memory and then dispose of the unmanaged memory when done.

using namespace System;
using namespace System::Runtime::InteropServices;

#include <iostream>                                                 // for printf


int main()
{
    // Create a managed string.
    String^ managedString = "Hello unmanaged world (from the managed world).";

    // Marshal the managed string to unmanaged memory.
    char* stringPointer = (char*) Marshal::StringToHGlobalAnsi(managedString ).ToPointer();

    printf("stringPointer = %s\n", stringPointer);

    // Always free the unmanaged string.
    Marshal::FreeHGlobal(IntPtr(stringPointer));

    return 0;
}
using System;
using System.Runtime.InteropServices;

class MainFunction
{
    static void Main()
    {
    Console.WriteLine("\nStringToGlobalAnsi\n");

    // Create a managed string.
    String  managedString = "I am a managed String";
    Console.WriteLine("1) managedString = " + managedString );

    // Marshal the managed string to unmanaged memory.
    IntPtr stringPointer = (IntPtr)Marshal.StringToHGlobalAnsi(managedString);
    Console.WriteLine("2) stringPointer = {0}", stringPointer );

    // Get the string back from unmanaged memory
    String RetrievedString = Marshal.PtrToStringAnsi( stringPointer);
    Console.WriteLine("3) Retrieved from unmanaged memory = " + RetrievedString );

    // Always free the unmanaged string.
    Marshal.FreeHGlobal(stringPointer);

    // IntPtr handle value is still the same:
    Console.WriteLine("4) stringPointer = " + stringPointer );

    // However, it contains no data after being freed:
    String RetrievedString2 = Marshal.PtrToStringAnsi( stringPointer);
    Console.WriteLine("5) RetrievedString2 = " + RetrievedString2 );
    }
}

Remarks

You can use FreeHGlobal to free any memory from the global heap allocated by AllocHGlobal, ReAllocHGlobal, or any equivalent unmanaged API method. If the hglobal parameter is IntPtr.Zero the method does nothing.

FreeHGlobal exposes the LocalFree function from Kernel32.DLL, which frees all bytes so that you can no longer use the memory pointed to by hglobal.

In addition to FreeHGlobal, the Marshal class provides two other memory-deallocation API methods: DestroyStructure and FreeCoTaskMem.

Security

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

Applies to

See also