UnmapViewOfFile

UnmapViewOfFile is a Windows API function in Kernel32.dll that unmaps a mapped view of a file from the calling process’s address space. It is used after a program has mapped a file into memory using MapViewOfFile, MapViewOfFileEx, or related functions such as MapViewOfFile3. The function signature is BOOL UnmapViewOfFile(LPCVOID lpBaseAddress), where lpBaseAddress is the base address of the mapped view returned by the mapping call.

On success, UnmapViewOfFile returns a nonzero value. On failure, it returns zero and extended error information is available via GetLastError. The operation affects only the calling process: unmapping a view in one process does not unmap views in other processes, even if those processes map the same file. Unmapping decreases the per-process reference for that view; if no views remain in the process, the corresponding resources may be freed. UnmapViewOfFile does not close the file-mapping object itself; the object may still exist if other mappings or handles remain.

Common error conditions include passing a pointer that does not refer to a mapped view in the calling process’s address space, in which case GetLastError may return ERROR_INVALID_ADDRESS. The function is a low-level operation that interacts with the system’s memory manager and is typically used to ensure proper release of resources when a memory-mapped file is no longer needed.

See also MapViewOfFile, MapViewOfFileEx, MapViewOfFile3, CreateFileMapping, OpenFileMapping.