"Width" of character on screen

Question

I'm using Ncurses to write text editor. I would like to know if there is a way to determine how many different characters can be placed on screen, where each of the character is encoded with UTF-8. For example when I get screen width of 10 and one row, I can put 10 characters of width 1 with values as below:

0123456789

But when I would like to put whole row of smiling faces I can only put 4 of those, on screen of size 10:

So in this example smiling face takes width of 2,5 on screen. I would like to know is there a way to determine width of character on the screen?

isn't that determined by the font you are using? only if each char is the same width, you are able to know beforehand how wide a certain number of chars will be. — nada, Apr 08 '19 at 08:24
related: [std::setw and unicode character](https://stackoverflow.com/q/49858446/995714) — phuclv, Apr 09 '19 at 16:20

score 3 · Accepted Answer · answered Apr 08 '19 at 08:36

ncurses uses wcwidth to determine the number of columns that a "wide character" (usually a Unicode value) in a wchar_t uses. That might not be the same as what the terminal actually does, but if your locale (LC_CTYPE, etc.) is set consistently with the terminal's capabilities and configuration, the results are fairly consistent.

While wcwidth is a standard function, it is incompletely standardized (I could digress). Most implementations use tables that are updated periodically (one source of problems), terminal emulators may/may not be consistent, and fonts may not correspond to the values in wcwidth.

With all of that in mind, you can always ask ncurses (or some other implementation of X/Open Curses) how many columns on the screen it would use by writing into a window that you do not display. Lynx does this for example, in LYStrExtent0:

/*
 * Determine the number of cells the given string would take up on the screen,
 * limited (in the case of wide characters) by the maxCells parameter.
 *
 * If the returnCellNum parameter is TRUE, return the number of cells;
 * otherwise, return the length (limited by the len parameter) of the prefix of
 * the string that fits in maxCells cells.
 */

"Width" of character on screen

1 Answers1