Who knew about printf() in C being able to specify foreground/background colors?

Dogs · 11-21-2010, 04:35 PM

I got curious during the construction of my program to search for blocks of text that contain certain words, and wanted to print out blocks of text with the words I was searching for, initially, in ALL CAPS and seperated by tabs for easy identification. That got boring, though, so I thought, "Can printf do colors, too?"

Yes it can.... Who knew?

Code:

/*Text attributes
       0    All attributes off
       1    Bold on
       4    Underscore (on monochrome display adapter only)
       5    Blink on
       7    Reverse video on
       8    Concealed on

    Foreground colors
       30    Black
       31    Red
       32    Green
       33    Yellow
       34    Blue
       35    Magenta
       36    Cyan
       37    White

    Background colors
       40    Black
       41    Red
       42    Green
       43    Yellow
       44    Blue
       45    Magenta
       46    Cyan
       47    White
*/

Code:

	printf("%c[%d;%dmHello World%c[%dm\n",27,1,33,27,0);

Dark_Helmet · 11-21-2010, 05:30 PM

Well, I don't think that's printf() doing the color changing. Those are escape sequences interpreted by the terminal. So, what happens with that string of characters depends on what features the terminal supports.

paulsm4 · 11-21-2010, 06:49 PM

Yup - that's probably old DOS code that uses "ansi.sys". The giveaway was the "<esc>[" ANSI driver character sequence (esc == ASCII "27").

Like the song goes "As primitive as can be..."

You can read more about ansi/vt100 terminal control sequences here:
http://www.termsys.demon.co.uk/vtansi.htm

And who knows - it might even work in any random xterm window or command prompt you might try it on. Go for it!

Sergei Steshenko · 11-21-2010, 11:30 PM

Quote:

Originally Posted by paulsm4

...
And who knows - it might even work in any random xterm window or command prompt you might try it on. Go for it!

Why not ? http://en.wikipedia.org/wiki/ANSI_terminal

paulsm4 · 11-22-2010, 12:42 AM

Quote:

Q: Why not?

A: Because it's EQUALLY likely to NOT work in any random xterm window or command prompt you might try. There are arguably much better ways to accomplish the same thing.

IMHO...

JohnGraham · 11-22-2010, 04:03 AM

Quote:

Originally Posted by paulsm4

There are arguably much better ways to accomplish the same thing.

Just out of interest, what are they? It's just I've never heard of any way of colouring text without using aforementioned escape sequences.

H_TeXMeX_H · 11-22-2010, 04:54 AM

Interesting ... not that useful, but interesting. You can try it out in awk as well, it has compatible syntax.

orgcandman · 11-22-2010, 11:17 AM

Quote:

Originally Posted by JohnGraham

Just out of interest, what are they? It's just I've never heard of any way of colouring text without using aforementioned escape sequences.

For *nix systems, http://tldp.org/HOWTO/NCURSES-Progra...WTO/color.html

I believe that ncurses interprets the TERM variable, and references the terminfo definition from the termcap library. Since I don't use ncurses, I could be completely wrong on this, however.

Dogs · 11-22-2010, 11:32 PM

Fun topic. I'll give ncurses a try after this semester is done.