GlobalAlloc - Win32 Programmer's Reference

Overview

Group

Quick Info

Windows NT
Yes
Win95
Yes
Win32s
Yes
Import Library
kernel32.lib
Header File
winbase.h
Unicode
No
Platform Notes
GMEM_FIXED is expensive (locks pages) on Win32s - use GMEM_MOVEABLE

GlobalAlloc

The GlobalAlloc function allocates the specified number of bytes from the heap. In the linear Win32 API environment, there is no difference between the local heap and the global heap.

HGLOBAL GlobalAlloc(

UINT uFlags,	// object allocation attributes
DWORD dwBytes	// number of bytes to allocate
);

Parameters
uFlags

Specifies how to allocate memory. If zero is specified, the default is GMEM_FIXED. Except for the incompatible combinations that are specifically noted, any combination of the following flags can be used. To indicate whether the function allocates fixed or movable memory, specify one of the first four flags:

Flag	Meaning
GMEM_FIXED	Allocates fixed memory. This flag cannot be combined with the GMEM_MOVEABLE or GMEM_DISCARDABLE flag. The return value is a pointer to the memory block. To access the memory, the calling process simply casts the return value to a pointer.
GMEM_MOVEABLE	Allocates movable memory. This flag cannot be combined with the GMEM_FIXED flag. The return value is the handle of the memory object. The handle is a 32-bit quantity that is private to the calling process. To translate the handle into a pointer, use the GlobalLock function.
GPTR	Combines the GMEM_FIXED and GMEM_ZEROINIT flags.
GHND	Combines the GMEM_MOVEABLE and GMEM_ZEROINIT flags.
GMEM_DDESHARE	Allocates memory to be used by the dynamic data exchange (DDE) functions for a DDE conversation. Unlike Windows version 3. x, this memory is not shared globally. However, this flag is available for compatibility purposes. It may be used by some applications to enhance the performance of DDE operations and should, therefore, be specified if the memory is to be used for DDE. Only processes that use DDE or the clipboard for interprocess communications should specify this flag.
GMEM_DISCARDABLE	Allocates discardable memory. This flag cannot be combined with the GMEM_FIXED flag. Some Win32-based applications may ignore this flag.
GMEM_LOWER	Ignored. This flag is provided only for compatibility with Windows version 3. x.
GMEM_NOCOMPACT	Does not compact or discard memory to satisfy the allocation request.
GMEM_NODISCARD	Does not discard memory to satisfy the allocation request.
GMEM_NOT_BANKED	Ignored. This flag is provided only for compatibility with Windows version 3. x.
GMEM_NOTIFY	Ignored. This flag is provided only for compatibility with Windows version 3. x.
GMEM_SHARE	Same as the GMEM_DDESHARE flag.
GMEM_ZEROINIT	Initializes memory contents to zero.

dwBytes

Specifies the number of bytes to allocate. If this parameter is zero and the uFlags parameter specifies the GMEM_MOVEABLE flag, the function returns a handle to a memory object that is marked as discarded.

Return Values
If the function succeeds, the return value is the handle of the newly allocated memory object.

If the function fails, the return value is NULL. To get extended error information, call GetLastError.

Remarks
If the heap does not contain sufficient free space to satisfy the request, GlobalAlloc returns NULL.

Because NULL is used to indicate an error, virtual address zero is never allocated. It is, therefore, easy to detect the use of a NULL pointer.

All memory is created with execute access; no special function is required to execute dynamically generated code.

Memory allocated with this function is guaranteed to be aligned on an 8-byte boundary.

The GlobalAlloc and LocalAlloc functions are limited to a combined total of 65,536 handles for GMEM_MOVEABLE and LMEM_MOVEABLE memory per process. This limitation does not apply to GMEM_FIXED or LMEM_FIXED memory.

If this function succeeds, it allocates at least the amount of memory requested. If the actual amount allocated is greater than the amount requested, the process can use the entire amount. To determine the actual number of bytes allocated, use the GlobalSize function.

See Also
GlobalFree, GlobalLock, GlobalReAlloc, GlobalSize, LocalAlloc

Programming books recommended by Amazon.com

More programming books on Amazon.com

Share this page

Tweet
Follow us

Last news from Greatis Software

    Nostalgia .Net     .Net is powerful, but not all-powerful, so sometimes we need to use Win32 API for our .Net applications. It's simple enough with Platform Invoke if you have Win32 skill, but we do not always have time to dig the ancient documentation, declare the special types that are compatible with Win32, find the values of the Win32's constants and so on. Nostalgia .Net offers several simple-to-use classes, and components that will allow you to forget about the headache of Win32 and just use the power of Win32 in your application the same way as you use the native. Net classes. More »

Recommended software for developers

    Ultimate Pack     Component pack for Delphi and C++ Builder that contains runtime form designer, runtime object inspector, print suite and much more for the very special price. More »

    Form Designer .Net     Unique runtime form design solution that allows to edit any form in .Net WinForms application at runtime with full source codes for only 300 euro! More »

    Print Suite .Net     Print Suite .Net is a set of components for easy printing texts, images and grids from your WinForms applications. Full C# source codes are available More »

    Gradient Controls .Net     Gradient Controls .Net offers controls with gradient background feature. Labels, panels and so on... Full C# source codes are available More »

    Greatis iGrid     iGrid plots drawing grid right over your desktop, so you can use it everywhere, with any drawing application without any special plugins for different graphic editors. More »

All the contacts and projects

Dmitry Vasiliev (just.dmitry)

More Online Helps

Win32 Programmer's Reference
Win32 Multimedia Programmer's Reference
OLE Programmer's Reference
Microsoft Windows Pen API Programmer's Reference
Microsoft Windows Sockets 2 Reference
Microsoft Windows Telephony API (TAPI) Programmer's Reference
Unix Manual Pages