MapViewOfFile

MapViewOfFile is a Windows API function that maps a view of a file mapping object into the virtual address space of the calling process. It allows programs to access the contents of a file (or paging file backed memory) through memory rather than explicit I/O calls. This function is typically used after a file mapping object has been created with CreateFileMapping (or opened with OpenFileMapping).

The function takes a handle to a file mapping object, a desired access flag, the high and low parts of the file offset, and the number of bytes to map. The offset specifies where the mapping starts within the file, and the number of bytes to map can be zero to map the entire remainder of the mapping from the offset. The file offset must be aligned to the system’s allocation granularity. The return value is a pointer to the base address of the mapped view, which the process can use like ordinary memory.

Access rights are controlled by dwDesiredAccess, which can include flags such as FILE_MAP_READ, FILE_MAP_WRITE, and FILE_MAP_EXECUTE, among others. The requested access must be compatible with the protections of the underlying mapping object. On success, MapViewOfFile returns a pointer to the mapped region. On failure, it returns NULL and one can use GetLastError to obtain the error code.

To use and release resources properly, the mapped view should be unmapped with UnmapViewOfFile when it is no longer needed, and the file mapping object handle should be closed with CloseHandle. Multiple processes can share a mapping if they have a handle to the same mapping object or have opened it by name.