VirtualQuery

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

To obtain information about a range of pages in the address space of another process, use the VirtualQueryEx function.

DWORD VirtualQuery(
  LPCVOID lpAddress,                   // address of region
  PMEMORY_BASIC_INFORMATION lpBuffer,  // information buffer
  DWORD dwLength                       // size of buffer
);

Parameters

lpAddress

[in] 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

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

dwLength

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

Return Values

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

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 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 reserved by a call to the VirtualAlloc function.
• The access of all pages is the same with 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 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 40 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 30 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.

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, GetSystemInfo, MEMORY_BASIC_INFORMATION, VirtualQueryEx