ULONGLONG

ULONGLONG is a Windows-specific data type that represents an unsigned 64-bit integer. It is defined in Windows header files, such as WinNT.h and Windows.h, as a typedef alias for unsigned long long. In practice, ULONGLONG is used by the Windows API to denote 64-bit quantities in a way that preserves semantics across compilers and calling conventions.

As a mapping to the standard C/C++ type, ULONGLONG corresponds to unsigned long long on most compilers, and is often paired with its signed counterpart LONGLONG. For portable code, the standard fixed-width type uint64_t from stdint.h can be used, with Windows API types cast or typedef’d as needed.

Size and range: ULONGLONG is 64 bits wide, with a value range from 0 to 18446744073709551615 inclusive.

Usage notes: Include Windows.h or WinNT.h when using ULONGLONG in Windows applications. Many Windows APIs accept parameters of this type for file sizes, large counters, and other 64-bit data. When writing cross-platform code, prefer standard types or conditional typedefs to ensure portability.

See also: LONGLONG, the signed 64-bit counterpart; unsigned long long, the standard C/C++ type that ULONGLONG aliases on Windows.

ULONGLONG is primarily found in the Windows API and is not a standard C or C++ type, but it remains a common historical synonym in Windows codebases for 64-bit unsigned integers.