wcwidth

wcwidth is a function defined in the C standard library that returns the number of column positions a wide character wc will occupy when displayed in a terminal. It is declared in wchar.h and is locale dependent; the current LC_CTYPE affects how widths are computed. The function is commonly used when rendering or wrapping text that contains wide or non-ASCII characters.

Return values and behavior: If wc is the null wide character L'\0', wcwidth returns 0. If the character is a combining mark or another zero-width character, the function also returns 0. If the character is a control character or otherwise not printable, wcwidth returns -1. For printable characters, the width is typically 1 for ordinary characters and 2 for East Asian wide or fullwidth characters, though the exact result can depend on the locale and the Unicode data used by the C library.

Related function: wcswidth computes the total display width of a null-terminated wide string (or up to a given length). Its signature is int wcswidth(const wchar_t *pwcs, size_t n). It sums the wcwidth values for up to n characters, returning -1 if any constituent character has width -1. This is helpful for line wrapping, indentation, and column alignment in text rendering.

Implementation and caveats: The results rely on the C library’s Unicode data and the active locale; different platforms and libraries may yield different widths for certain ambiguous characters. wcwidth and wcswidth do not account for grapheme cluster length, combining sequences, or contextual rendering beyond individual code points, so they can be incomplete for precise text layout in some languages.