VirtualQuery

This function provides information about a range of pages in the virtual address space of the calling process.

At a Glance

Header file:	Winbase.h
Windows CE versions:	1.0 and later

Syntax

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

Parameters

lpAddress

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.

lpBuffer

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

dwLength

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

Return Values

The actual number of bytes returned in the information buffer indicates success.

Remarks

VirtualQuery 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 with the MEM_COMMIT, MEM_RESERVE, MEM_FREE, MEM_PRIVATE, MEM_MAPPED, or MEM_IMAGE flag.
If the initial page is not free, all pages in the region are part of the same initial allocation of pages reserved by a call to the VirtualAlloc function.
The access of all pages is the same with the PAGE_READONLY, PAGE_READWRITE, PAGE_NOACCESS, PAGE_WRITECOPY, PAGE_EXECUTE, PAGE_EXECUTE_READ, PAGE_EXECUTE_READWRITE, PAGE_EXECUTE_WRITECOPY, PAGE_GUARD, or PAGE_NOCACHE flag.

The 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, in bytes, of the region of pages with matching attributes. For example, if there is a 20 megabyte (MB) region of free memory, and VirtualQuery 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 10 MB.

This function reports on a region of pages in the memory of the calling process, and the VirtualQueryEx function reports on a region of pages in the memory of a specified process.