Win32 Memory Management API

Core Memory Allocation Functions

These functions are fundamental for requesting and releasing blocks of memory from the system heap.

• VirtualAlloc

  Reserves or commits a region of pages in the virtual address space of the calling process.

• VirtualFree

  Releases, decommits, or both a region of pages within the process's virtual address space.

• VirtualAllocEx

  Reserves, commits, or changes the state of a region of pages in the virtual address space of a specified process.

• VirtualFreeEx

  Releases, decommits, or both a region of pages within the virtual address space of a specified process.

• HeapAlloc

  Allocates a specified number of bytes from the heap. The allocated memory is not initialized. If the function succeeds, it returns a pointer to the beginning of the allocated memory block.

• HeapFree

  Frees a specified batch of memory in the heap. If the function succeeds, the return value is nonzero.

Memory Information and Manipulation

Functions for querying memory status, protecting memory regions, and copying memory blocks.

• VirtualQuery

  Retrieves detailed information about a range of pages within the virtual address space of the calling process.

• VirtualProtect

  Changes the protection of an allocated region of the virtual address space of the calling process.

• memcpy

  Copies a specified number of bytes from a location in memory to another location in memory.

• memset

  Fills the first `n` bytes of the memory area pointed to by `s` with the specified `c` (first converted to an `unsigned char`).

Specific Memory API Details

VirtualAlloc

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

Parameters:

Parameter	Type	Description
lpAddress	LPVOID	The starting address of the region to allocate. If this parameter is NULL, the system determines where to allocate the region.
dwSize	SIZE_T	The size of the region to allocate, in bytes.
flAllocationType	DWORD	The type of memory allocation. This parameter can be one or more of the following values: MEM_COMMIT, MEM_RESERVE, MEM_RESET, MEM_RESET_UNDO, MEM_LARGE_PAGES, MEM_PHYSICAL, MEM_TOP_DOWN.
flProtect	DWORD	The memory protection for the region of pages to be allocated. This parameter can be one of the following values: PAGE_EXECUTE, PAGE_EXECUTE_READ, PAGE_EXECUTE_READWRITE, PAGE_EXECUTE_WRITECOPY, PAGE_NOACCESS, PAGE_READONLY, PAGE_READWRITE, PAGE_WRITECOPY, PAGE_TARGETS_INVALID, PAGE_TARGETS_NO_UPDATE.

Return Value:

If the function succeeds, it returns a pointer to the allocated region. Otherwise, it returns NULL.

VirtualFree

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

Parameters:

Parameter	Type	Description
lpAddress	LPVOID	A pointer to the starting address of the region of pages to be freed.
dwSize	SIZE_T	The size of the region to free, in bytes. This parameter must be 0 if dwFreeType is MEM_RELEASE.
dwFreeType	DWORD	The type of operation to perform on the specified memory region. This parameter can be one of the following values: MEM_DECOMMIT, MEM_RELEASE.

Return Value:

If the function succeeds, it returns TRUE. Otherwise, it returns FALSE.

HeapAlloc

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

Parameters:

Parameter	Type	Description
hHeap	HANDLE	A handle to the heap that was created by a call to the HeapCreate function.
dwFlags	DWORD	Flags that control the heap allocation. HEAP_GENERATE_EXCEPTIONS, HEAP_NO_SERIALIZE, HEAP_ZERO_MEMORY.
dwBytes	SIZE_T	The number of bytes to allocate from the heap.

Return Value:

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

VirtualQuery

SIZE_T VirtualQuery(
  LPCVOID                   lpAddress,
  PMEMORY_BASIC_INFORMATION lpBuffer,
  SIZE_T                    dwLength
);
            

Parameters:

Parameter	Type	Description
lpAddress	LPCVOID	A pointer to the starting address of the region of pages to be queried.
lpBuffer	PMEMORY_BASIC_INFORMATION	A pointer to a MEMORY_BASIC_INFORMATION structure that receives information about the region of pages.
dwLength	SIZE_T	The size of the buffer pointed to by lpBuffer, in bytes.

Return Value:

If the function succeeds, the return value is the number of bytes of information written to the buffer. If the function fails, the return value is 0.