0b

0b is a prefix used in several programming languages to denote that the following digits form a binary integer literal. When written as 0b followed by a sequence of 0s and 1s, the value is interpreted in base-2. The prefix is typically case-insensitive, so 0b and 0B are treated the same.

The 0b prefix is supported in a number of popular languages. In Python, 0b1010 evaluates to decimal 10; since Python 3.6, digits can include underscores for readability, as in 0b1010_0101. In JavaScript (ECMAScript 2015 and later), 0b11110000 denotes a binary integer. In Rust, binary literals use 0b and 0B, with the actual value determined by the type context.

Syntax and rules: A binary literal consists of the prefix 0b or 0B followed by digits restricted to 0 and 1. The exact treatment of the literal—such as its type, signedness, or width—depends on the language and the surrounding code. Some languages allow digit separators (like underscores) for readability, while others require continuous digits.

Limitations and context: The 0b prefix is not part of data interchange formats such as JSON, which do not define binary literals. It is primarily a programming-language feature used in source code and, where supported, compiled or interpreted accordingly.

See also: hexadecimal prefix 0x, numeral systems, binary literals.