Fixed-Width Types

Overview

Prior to C23, exact-width integer types were available. Since C23 bit-precise integer types have also been included.

Exact-Width

The <stdint.h> library contains exact-width integer types. These are aliases to types that represent an exact width and sign representation:

• If the type uintN_t is provided, it is an unsigned integer type with exactly $N$ bits of width and precision.
• If the type intN_t is provided, is is signed, with two's complement representation, has a width of exactly $N$ bits and a precision of $N-1$.

The C standard says these typedefs must be defined if they can be satisfied. Otherwise they may not exist.

Bit-Precise

Since C23, bit-precise integer types allow specifying quantities that should fit within a specified number of bits. The number of bits is provided as an argument to the _BitInt specifier.

Literal types may use case-insensitive suffix wb to specify signed bit-precise integer types. Likewise, case-insensitive suffix uwb specifies unsigned bit-precise integer types.

Since C23, additional bit operations have been made available in the <stdbit.h> header. These functions act on unsigned integer types.