MapViewOfFile

This function maps a view of a file into the address space of the calling process.

LPVOID MapViewOfFile( 
HANDLE hFileMappingObject, 
DWORD dwDesiredAccess, 
DWORD dwFileOffsetHigh, 
DWORD dwFileOffsetLow, 
DWORD dwNumberOfBytesToMap );

Parameters

• hFileMappingObject
  Handle to an open handle of a file-mapping object. The CreateFileMapping function returns this handle.

• dwDesiredAccess
  Specifies the type of access to the file view and, therefore, the protection of the pages mapped by the file. This parameter can be one of the following values:

  Value	Description
  FILE_MAP_WRITE	Read-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.

• 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 systems 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 systems memory allocation granularity.

• dwNumberOfBytesToMap
  Specifies the number of bytes of the file to map. If dwNumberOfBytesToMap is zero, the entire file is mapped.

Return Values

The starting address of the mapped view indicates success. NULL indicates failure. To get extended error information, call GetLastError.

Remarks

The 64 KB alignment is not required for the dwFileOffsetLow parameter.

Mapping a file makes the specified portion of the file visible in the address space of the calling process.

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. In order to create another view of a file-mapping object for a different process, use the CreateFileMapping function.

A mapped view of a file is not guaranteed to be coherent with a file being accessed by the ReadFile or WriteFile function.

Note To guard against an access violation, use structured exception handling to protect any code that writes to or reads from a memory mapped view.

Requirements

Note   This API is part of the complete Windows CE OS package as provided by Microsoft. The functionality of a particular platform is determined by the original equipment manufacturer (OEM) and some devices may not support this API.

See Also

CreateFileMapping, GetSystemInfo, UnmapViewOfFile, SYSTEM_INFO

 Last updated on Tuesday, July 13, 2004

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