This function provides access to an area of shared memory.


SHLockShared (
    HANDLE hData,
    DWORD dwProcessId);


The hData argument is a handle to the shared memory.

The dwProcessId argument is the process identifier (PID) of the process that provides the context for interpreting the given handle.

Return Value

If successful, the function returns a pointer to the shared memory. Otherwise, the function returns NULL.


The function treats the hData and dwProcessId arguments as a pair that together identify the shared memory. In general, hData will have been the result of some earlier call to SHAllocShared (possibly in some other process) and dwProcessId will have been the last of the arguments given in that same call to SHAllocShared.

The handle refers to a file-mapping object that contains the shared memory. The function duplicates the given handle into the context of the current process and uses the duplicate to map a view of the file-mapping object into the address space of the current process. (The view has read-write access. To choose between read-only and read-write, use SHLockSharedEx.)


The SHLockShared function is exported from SHLWAPI.DLL as ordinal 8 in version 4.71 and higher.

Though this function dates from as long ago as 1997, it was still not documented by Microsoft in the MSDN Library at least as late as the CD edition dated January 2004.

The function also exists indirectly as an export from SHELL32.DLL. Indeed, this existence predates its implementation in SHLWAPI. The NT releases of SHELL32 version 4.00, as long ago as 1996, and all releases of later SHELL32 versions export SHLockShared as ordinal 521. From SHELL32 version 4.71, the implementation in SHELL32 is just a jump to the corresponding implementation imported from SHLWAPI. Late builds of SHELL32 version 6.00 export the function by name. This change may be related to Microsoft’s programme of documenting interfaces for compliance with a consent decree. A SHELL32 function named _SHLockShared was documented among the Settlement Program Interfaces in December 2002. The function is said there to require SHELL32 “version 5.0 or later”, as if to ignore three years or more of earlier existence.