Print Unicode characters in C, using ncurses

Question

I have to draw a box in C, using ncurses;

First, I have defined some values for simplicity:

#define RB "\e(0\x6a\e(B"  (ASCII 188,Right bottom, for example)

I have compiled with gcc, over Ubuntu, with -finput-charset=UTF-8 flag.

But, if I try to print with addstr or printw, I get the hexa code. What I`m doing wrong?

Answer 1

ncurses defines the values ACS_HLINE, ACS_VLINE, ACS_ULCORNER, ACS_URCORNER, ACS_LLCORNER and ACS_LRCORNER. You can use those constants in addch and friends, which should result in your seeing the expected box characters. (There's lots more ACS characters; you'll find a complete list in man addch.)

ncurses needs to know what it is drawing because it needs to know exactly where the cursor is all the time. Outputting console control sequences is not a good idea; if ncurses knows how to handle the sequence, it has its own abstraction for the feature and you should use that abstraction. The ACS ("alternate character set") defines are one of those abstractions.

Answer 2

A few issues:

• if your program writes something like "\e(0\x6a\e(B" using addstr, then ncurses (any curses implementation) will translate the individual characters to printable form as described in the addch manual page.
• ncurses supports line-drawing for commonly-used pseudo-graphics using symbols (such as ACS_HLINE) which are predefined characters with the A_ALTCHARSET attribute combined. You can read about those in the Line Graphics section of the addch manual page.
• the code 0x6a is ASCII j, which (given a VT100-style mapping) would be the lower left corner. The curses symbol for that is ACS_LRCORNER.
• you cannot write the line-drawing characters with addstr; instead addch, addchstr are useful. There are also functions oriented to line-drawing (see box and friends).

• running in Ubuntu, your locale encoding is probably UTF-8. To make your program work properly, it should initialize the locale as described in the Initialization section of the ncurses manual page. In particular:

  setlocale(LC_ALL, "");

  Also, your program should link against the ncursesw library (-lncursesw) to use UTF-8, rather than just ncurses (-lncurses).

• when compiling on Ubuntu, to use the proper header definitions, you should define _GNU_SOURCE.

Answer 3

BTW, maybe I'm probably arriving somewhat late to the party but I'll give you some insight that might or not shed some light and skills for your "box drawing" needs.

As of 2020 I'm involved in a funny project on my own mixing Swift + Ncurses (under OSX for now, but thinking about mixing it with linux). Apparently it works flawlessly.

The thing is, as I'm using Swift, internally it all reduces to "importing .h and .c" files from some Darwin.ncurses library the MacOS Xcode/runtime offers.

That means (I hope) my newly acquired skills might be useful for you because apparently we're using the very same .h and .c files for our ncurses needs. (or at least they should be really similar)

Said that:

---

As of now, I "ignored" ACS_corner chars (I can't find them under swift/Xcode/Darwin.ncurses runtime !!!) in favour of pure UTF "corner chars", which also exist in the unicode pointspace, look:

https://en.wikipedia.org/wiki/Box-drawing_character

What does it mean? Whenever I want to use some drawing box chars around I just copy&paste pure UTF-8 chars into my strings, and I send these very strings onto addstr.

Why does it work? Because as someone also answered above, before initializing ncurses with initscr(), I just claimed "I want a proper locale support" in the form of a setlocale(LC_ALL, ""); line.

What did I achieve? Apparently pure magic. And very comfortable one, as I just copy paste box chars inside my normal strings. At least under Darwin.ncurses/OSX Mojave I'm getting, not only "bounding box chars", but also full UTF8 support.

Try the "setlocale(LC_ALL, ""); initscr();" approach and tell us if "drawing boxes" works also for you under a pure C environment just using UTF8 bounding box chars.

Greetings and happy ncursing!