Memory Allocation Functions

These functions are used to request memory blocks from the system's available memory pool.

VirtualAlloc

Description: Reserves or commits a region of pages in the virtual address space of the calling process. This is the primary function for flexible memory allocation.

Syntax:

LPVOID VirtualAlloc(
  LPVOID lpAddress,
  SIZE_T dwSize,
  DWORD  flAllocationType,
  DWORD  flProtect
);

Parameters:

Name	Type	Description
lpAddress	LPVOID	The starting address of the region of pages to be allocated. If NULL, the system determines where to allocate the region.
dwSize	SIZE_T	The size, in bytes, of the region of pages to be allocated.
flAllocationType	DWORD	The type of memory allocation. Can be MEM_COMMIT, MEM_RESERVE, or a combination.
flProtect	DWORD	The memory protection for the region of pages. Can be PAGE_READWRITE, PAGE_EXECUTE_READWRITE, etc.

Return Value: If the function succeeds, the return value is a pointer to the allocated region of pages. If the function fails, the return value is NULL.

HeapAlloc

Description: Allocates a block of memory from a specified heap. This function is generally faster for frequent allocations than VirtualAlloc.

Syntax:

LPVOID HeapAlloc(
  HANDLE hHeap,
  DWORD  flOptions,
  SIZE_T dwBytes
);

Parameters:

Name	Type	Description
hHeap	HANDLE	A handle to the heap. This handle is returned by the HeapCreate function.
flOptions	DWORD	Heap allocation options. Can be HEAP_ZERO_MEMORY.
dwBytes	SIZE_T	The number of bytes to allocate.

Return Value: If the function succeeds, it returns a pointer to the allocated memory. If the function fails, it returns NULL.

Memory Deallocation Functions

These functions are used to release memory previously allocated by the system.

VirtualFree

Description: Releases, decommits, or both pages in the calling process's virtual address space. It can also decommit and release memory pages.

Syntax:

BOOL VirtualFree(
  LPVOID lpAddress,
  SIZE_T dwSize,
  DWORD  dwFreeType
);

Parameters:

Name	Type	Description
lpAddress	LPVOID	A pointer to the starting address of the region of pages to be freed. This address must be the base address returned by VirtualAlloc or a base address followed by an offset.
dwSize	SIZE_T	The size, in bytes, of the region of pages to be freed. This parameter is ignored if dwFreeType is MEM_RELEASE.
dwFreeType	DWORD	The type of memory freeing operation. Can be MEM_DECOMMIT or MEM_RELEASE.

Return Value: If the function succeeds, the return value is TRUE. If the function fails, the return value is FALSE.

HeapFree

Description: Frees a memory block previously allocated by a call to the HeapAlloc or HeapReAlloc function. The memory block must be from the heap specified by the hHeap parameter.

Syntax:

BOOL HeapFree(
  HANDLE hHeap,
  DWORD  flOptions,
  LPVOID lpMem
);

Parameters:

Name	Type	Description
hHeap	HANDLE	A handle to the heap. This handle is returned by the HeapCreate function.
flOptions	DWORD	Heap freeing options. Must be 0.
lpMem	LPVOID	A pointer to the memory block to be freed. This pointer is returned by HeapAlloc or HeapReAlloc.

Return Value: If the function succeeds, the return value is TRUE. If the function fails, the return value is FALSE.

Memory Information Functions

These functions retrieve information about the memory usage of a process.

GlobalMemoryStatusEx

Description: Fills a MEMORYSTATUSEX structure with information about the current memory usage of the computer. This includes information about physical memory, virtual memory, and page file usage.

Syntax:

BOOL GlobalMemoryStatusEx(
  LPMEMORYSTATUSEX lpBuffer
);

Parameters:

Name	Type	Description
lpBuffer	LPMEMORYSTATUSEX	A pointer to a MEMORYSTATUSEX structure that receives information about the current memory status.

Return Value: If the function succeeds, the return value is TRUE. If the function fails, the return value is FALSE.