ASCII 0 — NUL

The NUL character is the null byte, originally used as padding for mechanical teletype machines to allow time for the carriage to return. In C and C++, NUL (written as '\0') terminates strings, making it foundational to memory management and buffer handling. Null-terminated strings are so pervasive they are called C strings. Buffer overflow vulnerabilities and null byte injection attacks exploit NUL handling, making it one of the most security-critical characters in computing history.

Control characters were defined in the original 1963 ASCII standard to manage telecommunications equipment and terminal devices. Unlike printable characters representing visible symbols, control codes perform actions: initiating transmissions, acknowledging received data, triggering device alerts, and structuring information hierarchically. Of ASCII's 128 code points, 33 are designated as control characters (codes 0–31 plus 127), reflecting the standard's deep roots in telegraphy and serial communication systems. While most control codes have fallen out of daily use, several remain essential to modern computing workflows.

In the ASCII encoding table, Null is assigned code point 0 in decimal (0x00 hexadecimal, 000 octal, 00000000 binary). The 7-bit ASCII standard, first published in 1963 by the American Standards Association, defines exactly 128 characters that remain the foundation of text encoding systems worldwide. UTF-8, the dominant encoding on the modern web, is fully backward compatible with ASCII — every ASCII character is encoded as the identical single byte in UTF-8, guaranteeing that Null works reliably across all operating systems, programming languages, and internet protocols.