LPDWORD

LPDWORD is a Windows API data type defined as a pointer to a DWORD. DWORD is a 32-bit unsigned integer used throughout the Win32 API. In headers, LPDWORD is defined as DWORD*, making it a pointer to a 32-bit value.

LPDWORD is commonly used as an output parameter in Win32 functions. Many API calls write a value into a DWORD via a pointer passed by the caller, such as the number of bytes read or written, the size of data retrieved, or a status count. The caller must provide the address of a DWORD variable; upon return, the function stores the result at that location and the caller can read it.

In C and C++, LPDWORD is equivalent to DWORD*. Code examples typically declare a DWORD variable and pass its address to the function, e.g., using a variable like dw and passing &dw as the LPDWORD argument. This usage pattern reflects the API’s convention of using output parameters to return additional information beyond a function’s primary return value.

Platform considerations: DWORD and LPDWORD are 32-bit types, a design choice that remains consistent on 64-bit Windows. This ensures that the pointer type represents a 32-bit memory area regardless of the overall process or pointer width.

Related notes: LPDWORD is part of the Windows API’s traditional LP (long pointer) type naming system. While modern code may prefer standard C or C++ types, LPDWORD continues to appear in numerous Windows headers and documentation for compatibility with existing APIs.