CHARBIT

CHARBIT is a term used to describe the number of bits used to represent a character in a computer system. In formal C and C++ terminology, the precise reference is the macro named CHAR_BIT, defined in the standard header limits.h. CHAR_BIT specifies the number of bits in a byte as used by the language, i.e., the number of bits in the char type. The value is implementation-defined but generally at least 8; on most modern systems it is 8, while some historical or specialized architectures have used 7, 9, or more bits per byte.

In practice, CHAR_BIT is used to calculate the total number of bits in a given type by multiplying the number of chars by CHAR_BIT, since sizeof(char) is defined to be 1. For example, the number of bits in an int is sizeof(int) multiplied by CHAR_BIT. This macro underpins low-level programming tasks such as bit packing, serialization, and cross-platform data layout checks, where exact bit counts matter.

Limitations and considerations: CHAR_BIT reflects the chip’s byte size, not the width of a machine word. Code that assumes CHAR_BIT equals 8 may fail on systems where it differs. While CHAR_BIT has become 8 on most contemporary platforms, portable software often avoids hard-coded assumptions about byte size and instead relies on CHAR_BIT when precise bit calculations are needed.

See also: CHAR_MAX, CHAR_MIN, limits.h, and related macros for integral types.