nonprintables

Nonprintables are characters that do not produce a visible symbol when text is rendered. In computing, they are primarily control and formatting characters that govern device operation, text layout, or data processing rather than display a glyph themselves.

Common examples include ASCII control characters in the C0 set (codes 0–31) and the delete character (code 127), such as NUL, BEL, BS, HT, LF, and CR. In Unicode, additional nonprinting characters exist in the control and formatting blocks, such as the zero-width space (U+200B), left-to-right mark (U+200E), and various nonspacing or enclosing marks. These characters may influence line breaks, directionality, or spacing without providing a visible symbol by themselves.

Impact and usage: Nonprintables are essential for encoding, communication protocols, and document processing. They can complicate text rendering, parsing, and search, and they may introduce security or compatibility issues if not handled properly.

Handling: Software often detects nonprintables and either strips them, escapes them, or preserves them depending on context. Functions and libraries offer tests such as isprint or iswprint, and Unicode-aware approaches use character categories (for example Cf for formatting, Cc for control). In data sanitization, nonprintables are commonly removed from user input to prevent injection or corruption.

Nonprintables are distinct from printable letters, digits, punctuation, and symbols.