VirtualQueryEx function

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

Syntax

SIZE_T VirtualQueryEx(
  HANDLE                    hProcess,
  LPCVOID                   lpAddress,
  PMEMORY_BASIC_INFORMATION lpBuffer,
  SIZE_T                    dwLength
);

Parameters

hProcess

A handle to the process whose memory information is queried. The handle must have been opened with the PROCESS_QUERY_INFORMATION access right, which enables using the handle to read information from the process object. For more information, see Process Security and Access Rights.

lpAddress

A pointer to the base address of the region of pages to be queried. This value is rounded down to the next page boundary. To determine the size of a page on the host computer, use the GetSystemInfo function.

If lpAddress specifies an address above the highest memory address accessible to the process, the function fails with ERROR_INVALID_PARAMETER.

lpBuffer

A pointer to a MEMORY_BASIC_INFORMATION structure in which information about the specified page range is returned.

dwLength

The size of the buffer pointed to by the lpBuffer parameter, in bytes.

Return value

The return value is the actual number of bytes returned in the information buffer.

If the function fails, the return value is zero. To get extended error information, call GetLastError. Possible error values include ERROR_INVALID_PARAMETER.

Remarks

VirtualQueryEx provides information about a region of consecutive pages beginning at a specified address that share the following attributes:

  • The state of all pages is the same (MEM_COMMIT, MEM_RESERVE, MEM_FREE, MEM_PRIVATE, MEM_MAPPED, or MEM_IMAGE).
  • If the initial page is not free, all pages in the region are part of the same initial allocation of pages created by a single call to VirtualAlloc, MapViewOfFile, or one of the following extended versions of these functions: VirtualAllocEx, VirtualAllocExNuma, MapViewOfFileEx, MapViewOfFileExNuma.
  • The access granted to all pages is the same (PAGE_READONLY, PAGE_READWRITE, PAGE_NOACCESS, PAGE_WRITECOPY, PAGE_EXECUTE, PAGE_EXECUTE_READ, PAGE_EXECUTE_READWRITE, PAGE_EXECUTE_WRITECOPY, PAGE_GUARD, or PAGE_NOCACHE).
The VirtualQueryEx function determines the attributes of the first page in the region and then scans subsequent pages until it scans the entire range of pages, or until it encounters a page with a nonmatching set of attributes. The function returns the attributes and the size of the region of pages with matching attributes, in bytes. For example, if there is a 40 megabyte (MB) region of free memory, and VirtualQueryEx is called on a page that is 10 MB into the region, the function will obtain a state of MEM_FREE and a size of 30 MB.

If a shared copy-on-write page is modified, it becomes private to the process that modified the page. However, the VirtualQueryEx function will continue to report such pages as MEM_MAPPED (for data views) or MEM_IMAGE (for executable image views) rather than MEM_PRIVATE. To detect whether copy-on-write has occurred for a specific page, either access the page or lock it using the VirtualLock function to make sure the page is resident in memory, then use the QueryWorkingSet or QueryWorkingSetEx function to check the Shared bit in the extended working set information for the page. If the Shared bit is clear, the page is private.

Requirements

   
Minimum supported client Windows XP [desktop apps only]
Minimum supported server Windows Server 2003 [desktop apps only]
Target Platform Windows
Header memoryapi.h (include Windows.h, Memoryapi.h)
Library Kernel32.lib
DLL Kernel32.dll

See also

GetSystemInfo

MEMORY_BASIC_INFORMATION

MapViewOfFileEx

Memory Management Functions

Virtual Memory Functions

VirtualAllocEx

VirtualProtectEx