GlobalAlloc

The GlobalAlloc function allocates the specified number of bytes from the heap. Win32 memory management does not provide a separate local heap and global heap.

Note  The global functions are slower than other memory management functions and do not provide as many features. Therefore, new applications should use the heap functions. However, the global functions are still used with DDE and the clipboard functions.

HGLOBAL GlobalAlloc(
  UINT uFlags,     // allocation attributes
  SIZE_T dwBytes   // number of bytes to allocate
);

Parameters

uFlags

[in] Specifies how to allocate memory. If zero is specified, the default is GMEM_FIXED. This parameter can be one or more of the following values, except for the incompatible combinations that are specifically noted.

Value	Meaning
GHND	Combines GMEM_MOVEABLE and GMEM_ZEROINIT.
GMEM_FIXED	Allocates fixed memory. The return value is a pointer.
GMEM_MOVEABLE	Allocates movable memory. In Win32, memory blocks are never moved in physical memory, but they can be moved within the default heap. The return value is a handle to the memory object. To translate the handle into a pointer, use the GlobalLock function. This value cannot be combined with GMEM_FIXED.
GMEM_ZEROINIT	Initializes memory contents to zero.
GPTR	Combines GMEM_FIXED and GMEM_ZEROINIT.

The following values are obsolete.

Value	Meaning
GMEM_DDESHARE	Ignored. This value is provided only for compatibility with 16-bit Windows.
GMEM_DISCARDABLE	Ignored. This value is provided only for compatibility with 16-bit Windows. In Win32, you must explicitly call the GlobalDiscard function to discard a block. This value cannot be combined with GMEM_FIXED.
GMEM_LOWER	Ignored. This value is provided only for compatibility with 16-bit Windows.
GMEM_NOCOMPACT	Ignored. This value is provided only for compatibility with 16-bit Windows.
GMEM_NODISCARD	Ignored. This value is provided only for compatibility with 16-bit Windows.
GMEM_NOT_BANKED	Ignored. This value is provided only for compatibility with 16-bit Windows.
GMEM_NOTIFY	Ignored. This value is provided only for compatibility with 16-bit Windows.
GMEM_SHARE	Ignored. This value is provided only for compatibility with 16-bit Windows.

dwBytes

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

Return Values

If the function succeeds, the return value is a handle to 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.

Memory allocated with this function is guaranteed to be aligned on an 8-byte boundary. All memory is created with execute access; no special function is required to execute dynamically generated code.

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.

To free the memory, use the GlobalFree function.

Windows 95/98: The heap managers are designed for memory blocks smaller than four megabytes. If you expect your memory blocks to be larger than one or two megabytes, you can avoid significant performance degradation by using the VirtualAlloc or VirtualAllocEx function instead.

Requirements

  Windows NT/2000: Requires Windows NT 3.1 or later.
  Windows 95/98: Requires Windows 95 or later.
  Header: Declared in Winbase.h; include Windows.h.
  Library: Use Kernel32.lib.

See Also

Memory Management Overview, Memory Management Functions, GlobalDiscard, GlobalFree, GlobalLock, GlobalSize