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Overview |
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Group |
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Quick Info
Windows NT
| Yes
| Win95
| Yes
| Win32s
| Yes
| Import Library
| kernel32.lib
| Header File
| winbase.h
| Unicode
| No
| Platform Notes
| Windows 95: Memory mapped files appear in the same address space in all
processes
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MapViewOfFileEx
The MapViewOfFileEx function maps a view of a file into the address space of the calling process.
This extended function allows the calling process to specify a suggested
memory address for the mapped view.
This function is available for Win32-based applications only.
LPVOID MapViewOfFileEx(
HANDLE hFileMappingObject,
| // file-mapping object to map into address space
| DWORD dwDesiredAccess,
| // access mode
| DWORD dwFileOffsetHigh,
| // high-order 32 bits of file offset
| DWORD dwFileOffsetLow,
| // low-order 32 bits of file offset
| DWORD dwNumberOfBytesToMap,
| // number of bytes to map
| LPVOID lpBaseAddress
| // suggested starting address for mapped view
| );
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Parameters
hFileMappingObject
Identifies an open handle to a file-mapping object. The CreateFileMapping and OpenFileMapping functions return this handle.
dwDesiredAccess
Specifies the type of access to the file-mapping object and, therefore, the
page protection of the pages mapped by the file. This parameter can be one of the
following values:
Value
| Meaning
| FILE_MAP_WRITE
| Read-and-write access. The hFileMappingObject parameter must have been created with PAGE_READWRITE protection. A read-write
view of the file is mapped.
| FILE_MAP_READ
| Read-only access. The hFileMappingObject parameter must have been created with PAGE_READWRITE or PAGE_READONLY
protection. A read-only view of the file is mapped.
| FILE_MAP_ALL_ACCESS
| Same as FILE_MAP_WRITE.
| FILE_MAP_COPY
| Copy on write access. If you create the map with PAGE_WRITECOPY and the view
with FILE_MAP_COPY, you will receive a view to the file. If you write to it, the
pages are automatically swappable and the modifications you make will not go
to the original data file.
Windows 95: You must pass PAGE_WRITECOPY to CreateFileMapping; otherwise, an error will be returned.
If you share the mapping between multiple processes using DuplicateHandle or OpenFileMapping and one process writes to a view, the modification is propagated to the other
process. The original file does not change.
Windows NT: There is no restriction as to how the hFileMappingObject parameter must be created. Copy on write is valid for any type of view.
If you share the mapping between multiple processes using DuplicateHandle or OpenFileMapping and one process writes to a view, the modification is not propagated to the
other process. The original file does not change.
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dwFileOffsetHigh
Specifies the high-order 32 bits of the file offset where mapping is to begin.
dwFileOffsetLow
Specifies the low-order 32 bits of the file offset where mapping is to begin.
The combination of the high and low offsets must specify an offset within the
file that matches the system's memory allocation granularity, or the function
fails. That is, the offset must be a multiple of the allocation granularity. Use
the GetSystemInfo function, which fills in the members of a SYSTEM_INFO structure, to obtain the system's memory allocation granularity.
dwNumberOfBytesToMap
Specifies the number of bytes of the file to map. If dwNumberOfBytesToMap is zero, the entire file is mapped.
lpBaseAddress
Points to the memory address in the calling process's address space where
mapping should begin. This must be a multiple of the system's memory allocation
granularity, or the function fails. Use the GetSystemInfo function, which fills in the members of a SYSTEM_INFO structure, to obtain the system's memory allocation granularity. If there is
not enough address space at the specified address, the function fails.
If lpBaseAddress is NULL, the operating system chooses the mapping address. In this case, this
function is equivalent to the MapViewOfFile function.
Return Values
If the function succeeds, the return value is the starting address of the
mapped view.
If the function fails, the return value is NULL. To get extended error
information, call GetLastError.
Remarks
Mapping a file makes the specified portion of the file visible in the address
space of the calling process.
If a suggested mapping address is supplied, the file is mapped at the
specified address (rounded down to the nearest 64K boundary) if there is enough address
space at the specified address. If there is not, the function fails.
Typically, the suggested address is used to specify that a file should be
mapped at the same address in multiple processes. This requires the region of
address space to be available in all involved processes. No other memory allocation,
including use of the VirtualAlloc function to reserve memory, can take place in the region used for mapping.
Windows 95: If the lpBaseAddress parameter specifies a base offset, the function succeeds only if the same
memory region is available for the memory mapped file in all other 32-bit
processes.
Windows NT: If the lpBaseAddress parameter specifies a base offset, the function succeeds if the given memory
region is not already in use by the calling process. the system does not guarantee that the same memory region is available for the memory mapped file
in other 32-bit processes.
Multiple views of a file (or a file-mapping object and its mapped file) are
said to be "coherent" if they contain identical data at a specified time. This
occurs if the file views are derived from the same file-mapping object. A process
can duplicate a file-mapping object handle into another process by using the DuplicateHandle function, or another process can open a file-mapping object by name by using
the OpenFileMapping function.
A mapped view of a file is not guaranteed to be coherent with a file being
accessed by the ReadFile or WriteFile function.
See Also
CreateFileMapping, DuplicateHandle, GetSystemInfo, MapViewOfFile, OpenFileMapping, ReadFile, UnmapViewOfFile, SYSTEM_INFO, VirtualAlloc, WriteFile
Related Links
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