| 术语 | virtualalloc |
| 释义 | VirtualAlloc 语法： C++ LPVOID WINAPI VirtualAlloc( __in_opt LPVOID lpAddress, __in SIZE_T dwSize, __in DWORD flAllocationType, __in DWORD flProtect ); VirtualAlloc函数 储备或犯有在调用进程的虚拟地址空间的页面区域。这个函数分配内存是自动初始化为零，除非MEM_RESET是指定的。 分配在另一个进程的地址空间的内存，使用VirtualAllocEx函数。 参数 lpAddress [中，可选] 该区域的起始地址分配。如果内存被保留，在指定的地址是四舍五入到最接近多种分配粒度。如果内存已经预留，并正在实施，该地址是向下舍入到下一个页面边界。要确定在主机上的页面大小和粒度的分配，使用的GetSystemInfo函数。如果该参数是NULL，系统确定如何分配该地区。 dwSize [in] 该区域的大小，以字节。如果lpAddress参数为NULL，这个值四舍五入到下一个页面边界。否则，分配的网页中包含的所有网页包含从lpAddress到lpAddress的一个或更多的字节+ dwSize。这意味着，2个字节的范围跨越边界的页面都将导致在分配区域内的网页。 flAllocationType [in] 内存分配的类型。此参数必须包含下列值之一。 ValueMeaning MEM_COMMIT 0x1000Allocates物理存储在内存中，或在指定保留在磁盘上的内存页分页文件。该函数初始化内存为0。 为了保留和提交一步，调用MEM_COMMIT VirtualAlloc | MEM_RESERVE页。 函数失败如果您尝试提交一个尚未被预留页面。由此产生的错误代码是ERROR_INVALID_ADDRESS。 企图犯下一个已经承诺不会导致函数失败页面。这意味着您可以提交首先确定每一页的页当前状态的承诺。 MEM_RESERVE 0x2000Reserves没有分配任何实际的物理存储在内存或磁盘上的分页文件的进程的虚拟地址空间范围。 您可以提交到的后续调用VirtualAlloc函数保留网页。为了保留和提交一步，调用MEM_COMMIT VirtualAlloc | MEM_RESERVE页。 其他的内存分配功能，如malloc和LocalAlloc，不能使用的内存保留的范围，直到它被释放。 MEM_RESET 0x80000Indicates的数据由lpAddress和dwSize指定的内存范围已不再感兴趣。该网页不应该读出或写入页面文件。但是，内存块将再次使用以后，因此不应该decommitted。此值不能用于任何其他值。 使用此值不保证范围与MEM_RESET将包含零操作。如果您想范围包含零，承诺解除的内存，然后再次作出它。 当您指定MEM_RESET的VirtualAlloc函数忽略flProtect价值。但是，您仍然必须设置flProtect为有效保护的价值，如PAGE_NOACCESS。 VirtualAlloc返回一个错误如果您使用MEM_RESET和范围的内存映射到一个文件中。甲共同的看法是唯一可以接受的，如果它映射到一个页面文件。 此参数还可以指定下列值所示。 ValueMeaning MEM_LARGE_PAGES 0x20000000Allocates使用大内存页支持。 大小和对齐方式必须是大页的最低倍数。要获得此值，使用GetLargePageMinimum功能。 Windows XP/2000操作系统：这个标志是不支持。 MEM_PHYSICAL 0x400000Reserves一个地址范围，可用于映射地址窗口扩展(AWE)的网页。 此值必须与MEM_RESERVE，没有其他值。 MEM_TOP_DOWN 0x100000Allocates在尽可能高的内存地址。 MEM_WRITE_WATCH 0x200000Causes系统以跟踪写入页分配的地区。如果指定此值，您还必须指定MEM_RESERVE。 要检索的是已被写入因为该地区拨出或写入跟踪状态重置，调用GetWriteWatch函数网页的地址。要重置写跟踪状态，调用GetWriteWatch或ResetWriteWatch。写跟踪功能仍然启用了内存区域，直到该地区被释放。 Windows 2000中：这个标志是不支持。 flProtect [in] 对于该地区的页面内存保护分配。如果网页被承诺，您可以指定任何内存保护常量之一。 返回值 如果函数成功，返回值是分配的页面地区基址。 如果函数失败，返回值为NULL。为了获得更多错误信息，调用GetLastError。 备注 每一页都有一个关联的页面的状态。该VirtualAlloc函数可以执行以下操作： 凯明地区保留的网页 储备区域自由页 同时保留和提交的免费网页地区 VirtualAlloc不能保留保留网页。它可以提交一个已经承诺页面。这意味着您可以提交的页面范围，不论他们是否已经承诺，而功能也不会失败。 您可以使用VirtualAlloc保留的网页块，然后作出进一步要求VirtualAlloc实施从预留屏蔽个人网页。这使得一个进程，消耗体能储备不存储其虚拟地址空间范围，直到需要它。 如果lpAddress参数不是NULL，则函数使用lpAddress和dwSize参数来计算的页面区域分配。在整个的页面范围现状必须符合由参数指定的flAllocationType分配类型。否则，函数失败并没有的网页分配。这种兼容性要求，并不排除犯页面已经承诺，如前面提到的。 若要执行动态生成的代码，使用VirtualAlloc分配内存和VirtualProtect职能，授予PAGE_EXECUTE访问。 该VirtualAlloc函数可用于保留在一个特定进程的虚拟地址空间的地址窗口扩展(AWE)的内存区域。这种内存区域可以被用来映射到的虚拟内存不足的应用程序所需的物理页。在MEM_PHYSICAL和MEM_RESERVE值必须设置在AllocationType参数。该MEM_COMMIT值不能被设置。该网页的保护必须设置为PAGE_READWRITE。 VirtualFree函数可以承诺解除一个坚定的网页，发布页面的存储，也可以同时承诺解除和释放一个坚定的页面。它也可以释放保留的网页，使其成为一个自由页面。 实例 有关示例，请参见保留国和提交内存。 要求： 最低支持：client－Windows 2000专业版 最低支持server－Windows 2000服务器 HeaderWinbase.h(头文件：winuser.h) LibraryKernel32.lib DLLKernel32.dll 参见 内存管理功能 虚拟内存函数 VirtualAllocEx VirtualFree VirtualLock VirtualProtect VirtualQuery 如果有任何问题和意见，请发送给微软(wsddocfb@microsoft.com) 生成日期：2009年8月27日 ＝＝英文原文＝＝VirtualAlloc Function Reserves or commits a region of pages in the virtual address space of the calling process. Memory allocated by this function is automatically initialized to zero, unless MEM_RESET is specified. To allocate memory in the address space of another process, use the VirtualAllocEx function. Syntax C++ LPVOID WINAPI VirtualAlloc( __in_opt LPVOID lpAddress, __in SIZE_T dwSize, __in DWORD flAllocationType, __in DWORD flProtect ); Parameters lpAddress [in, optional] The starting address of the region to allocate. If the memory is being reserved, the specified address is rounded down to the nearest multiple of the allocation granularity. If the memory is already reserved and is being committed, the address is rounded down to the next page boundary. To determine the size of a page and the allocation granularity on the host computer, use the GetSystemInfo function. If this parameter is NULL, the system determines where to allocate the region. dwSize [in] The size of the region, in bytes. If the lpAddress parameter is NULL, this value is rounded up to the next page boundary. Otherwise, the allocated pages include all pages containing one or more bytes in the range from lpAddress to lpAddress+dwSize. This means that a 2-byte range straddling a page boundary causes both pages to be included in the allocated region. flAllocationType [in] The type of memory allocation. This parameter must contain one of the following values. ValueMeaning MEM_COMMIT 0x1000Allocates physical storage in memory or in the paging file on disk for the specified reserved memory pages. The function initializes the memory to zero. To reserve and commit pages in one step, call VirtualAlloc with MEM_COMMIT | MEM_RESERVE. The function fails if you attempt to commit a page that has not been reserved. The resulting error code is ERROR_INVALID_ADDRESS. An attempt to commit a page that is already committed does not cause the function to fail. This means that you can commit pages without first determining the current commitment state of each page. MEM_RESERVE 0x2000Reserves a range of the process's virtual address space without allocating any actual physical storage in memory or in the paging file on disk. You can commit reserved pages in subsequent calls to the VirtualAlloc function. To reserve and commit pages in one step, call VirtualAlloc with MEM_COMMIT | MEM_RESERVE. Other memory allocation functions, such as malloc and LocalAlloc , cannot use a reserved range of memory until it is released. MEM_RESET 0x80000Indicates that data in the memory range specified by lpAddress and dwSize is no longer of interest. The pages should not be read from or written to the paging file. However, the memory block will be used again later, so it should not be decommitted. This value cannot be used with any other value. Using this value does not guarantee that the range operated on with MEM_RESET will contain zeroes. If you want the range to contain zeroes, decommit the memory and then recommit it. When you specify MEM_RESET, the VirtualAlloc function ignores the value of flProtect. However, you must still set flProtect to a valid protection value, such as PAGE_NOACCESS. VirtualAlloc returns an error if you use MEM_RESET and the range of memory is mapped to a file. A shared view is only acceptable if it is mapped to a paging file. This parameter can also specify the following values as indicated. ValueMeaning MEM_LARGE_PAGES 0x20000000Allocates memory using large page support . The size and alignment must be a multiple of the large-page minimum. To obtain this value, use the GetLargePageMinimum function. Windows XP/2000: This flag is not supported. MEM_PHYSICAL 0x400000Reserves an address range that can be used to map Address Windowing Extensions (AWE) pages. This value must be used with MEM_RESERVE and no other values. MEM_TOP_DOWN 0x100000Allocates memory at the highest possible address. MEM_WRITE_WATCH 0x200000Causes the system to track pages that are written to in the allocated region. If you specify this value, you must also specify MEM_RESERVE. To retrieve the addresses of the pages that have been written to since the region was allocated or the write-tracking state was reset, call the GetWriteWatch function. To reset the write-tracking state, call GetWriteWatch or ResetWriteWatch . The write-tracking feature remains enabled for the memory region until the region is freed. Windows 2000: This flag is not supported. flProtect [in] The memory protection for the region of pages to be allocated. If the pages are being committed, you can specify any one of the memory protection constants . Return Value If the function succeeds, the return value is the base address of the allocated region of pages. If the function fails, the return value is NULL. To get extended error information, call GetLastError . Remarks Each page has an associated page state . The VirtualAlloc function can perform the following operations: Commit a region of reserved pages Reserve a region of free pages Simultaneously reserve and commit a region of free pages VirtualAlloc cannot reserve a reserved page. It can commit a page that is already committed. This means you can commit a range of pages, regardless of whether they have already been committed, and the function will not fail. You can use VirtualAlloc to reserve a block of pages and then make additional calls to VirtualAlloc to commit individual pages from the reserved block. This enables a process to reserve a range of its virtual address space without consuming physical storage until it is needed. If the lpAddress parameter is not NULL, the function uses the lpAddress and dwSize parameters to compute the region of pages to be allocated. The current state of the entire range of pages must be compatible with the type of allocation specified by the flAllocationType parameter. Otherwise, the function fails and none of the pages are allocated. This compatibility requirement does not preclude committing an already committed page, as mentioned previously. To execute dynamically generated code, use VirtualAlloc to allocate memory and the VirtualProtect function to grant PAGE_EXECUTE access. The VirtualAlloc function can be used to reserve an Address Windowing Extensions (AWE) region of memory within the virtual address space of a specified process. This region of memory can then be used to map physical pages into and out of virtual memory as required by the application. The MEM_PHYSICAL and MEM_RESERVE values must be set in the AllocationType parameter. The MEM_COMMIT value must not be set. The page protection must be set to PAGE_READWRITE. The VirtualFree function can decommit a committed page, releasing the page's storage, or it can simultaneously decommit and release a committed page. It can also release a reserved page, making it a free page. Examples For an example, see Reserving and Committing Memory . Requirements Minimum supported clientWindows 2000 Professional Minimum supported serverWindows 2000 Server HeaderWinbase.h (include Windows.h) LibraryKernel32.lib DLLKernel32.dll See Also Memory Management Functions Virtual Memory Functions VirtualAllocEx VirtualFree VirtualLock VirtualProtect VirtualQuery Send comments about this topic to Microsoft Build date: 8/27/2009 ＝＝原始网址＝＝http://msdn.microsoft.com/en-us/library/aa366887(VS.85).aspx\n |
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