0prefixed

0prefixed is a term used in computing to describe numeric literals that begin with a leading zero. In many languages and data formats, a leading zero signals that the value should be interpreted in a non-decimal base; octal is the most common historical meaning, though the exact interpretation depends on the language or protocol.

In programming languages, 0-prefixed literals have varied conventions. In C and C++, a leading 0 indicates octal, while 0x indicates hexadecimal; some environments also support 0b for binary. In JavaScript, a leading zero can denote octal in non-strict mode, though modern practice favors explicit prefixes such as 0o for octal and strict mode disallows old octal literals. In Python, the old form of 0-prefixed numbers indicated octal in Python 2; Python 3 uses the 0o prefix for octal. In Unix and Unix-like systems, file permissions are often written as octal numbers such as 0755 or 0644.

Data handling and portability considerations are important with 0prefixed numbers. Leading zeros can cause misinterpretation if the consumer expects decimal, so some formats disallow them or require explicit base prefixes. JSON, for example, prohibits unnecessary leading zeros in numbers. When precision and portability are required, it is advisable to use explicit prefixes (such as 0o for octal or 0x for hexadecimal) or to store values as strings when the leading zero conveys an identifier rather than a numeric value.

See also: octal numeral system, numeric literal, leading zero, base prefix.