int64t

int64t is commonly used to refer to the 64-bit signed integer type defined by the C and C++ standards as int64_t. It denotes an exact-width integer type whose width is 64 bits on all conforming implementations.

Definition and width: In C, int64_t is defined in stdint.h (C99 and later); in C++, it is defined in cstdint. It is an exact-width integer type, meaning its size is guaranteed to be 64 bits wherever it is supported. The typical range is from -9223372036854775808 to 9223372036854775807, reflecting two's-complement interpretation on most modern systems.

Portability and usage: int64_t provides a portable way to work with 64-bit integers across different platforms. For constants and I/O, the standard provides macros such as INT64_C, INT64_MIN, INT64_MAX, and the I/O macros PRId64 and PRIu64 from inttypes.h (or cinttypes in C++). Example: include <stdint.h> and <inttypes.h>, then declare int64_t x = 1234567890123456789; and print with printf("%" PRId64 "\n", x);.

Spelling note: The correct standard name is int64_t with an underscore. Some texts or code may misspell it as int64t, but that form is not standard. If portability issues arise on older tools, check compiler documentation to verify support for exact-width integer types.

Relation to similar types: The unsigned counterpart is uint64_t. Other fixed-width types include int32_t, int16_t, and their unsigned variants. While some platforms offer long or long long as 64-bit, using the exact-width types from stdint.h/cstdint is preferred for portable, well-defined behavior.