UINT64MAX

UINT64MAX refers to the maximum value representable by an unsigned 64-bit integer. In standard programming practice, the corresponding type is uint64_t, defined by the C standard library header stdint.h and by cstdint in C++. The portable macro that represents this maximum value is UINT64_MAX. Some informal references shorten or misname it as UINT64MAX, but the canonical name is UINT64_MAX.

The value of UINT64_MAX is 2^64 − 1, which equals 18446744073709551615 in decimal and 0xFFFFFFFFFFFFFFFF in hexadecimal. In binary terms, every one of the 64 bits is set to 1, making it the largest unsigned value possible for a 64-bit type. This macro is defined only if a 64-bit unsigned integer type exists on the platform.

Usage and considerations: UINT64_MAX is used for bounds checks, initialization, and defining limits in portable code that relies on fixed-width integer types. When writing numeric literals that represent this maximum, languages commonly require a suffix such as ULL to ensure the literal is treated as an unsigned 64-bit value (e.g., 18446744073709551615ULL or 0xFFFFFFFFFFFFFFFFULL).

Relation to standards: The macro is part of the standard integer-capacity limits defined for fixed-width types. It helps ensure consistent behavior across compilers and architectures that provide a 64-bit unsigned integer type. See also: UINT64_MAX, UINT32_MAX, UINTMAX_MAX, stdint.h, cstdint.