dualwidth

Dualwidth refers to the property of certain characters to occupy two columns in a fixed-width display, contrasting with the single column used by most Latin characters. It arises primarily in environments that render text on monospaced grids, such as terminal emulators and code editors, where East Asian scripts are commonly mixed with Western text. Characters that take two columns are typically those classified as fullwidth or wide in Unicode.

Unicode defines width properties for characters. The East Asian Width property uses categories such as F (fullwidth) and W (wide) to indicate two-column characters, while H (halfwidth) and Na (narrow) indicate one column. Ambiguous (A) and Neutral (N) characters may be treated as one or two columns depending on locale, font, or rendering settings. Diacritics and combining marks often have zero width and do not advance the cursor.

Rendering engines rely on width information from tables or libraries (for example, wcwidth) to compute the display width of strings, move the cursor, and wrap lines correctly. In addition to tangible characters, zero-width joiners and variation selectors can affect width calculations by altering grapheme composition without adding visible space.

Accurate dualwidth handling is important for text editors, terminals, data tables, and log displays that mix scripts. Misestimation can produce misaligned columns, broken layouts, or incorrect cursor positions. As a result, software commonly implements width-aware rendering to ensure consistent alignment across platforms and locales. See also East Asian Width, Fullwidth, Halfwidth, wcwidth, Unicode.