C macro generating strings by character code

Question

I'm working with a game engine that uses escape codes in strings to perform commands such as setting color. eg to set the color to red, you write "Red text:\x81\xFF\x00\x00\xFFhello!" (0x81, red, green, blue, alpha).

Is it possible to create a macro like TEXT_COLOR(r,g,b,a) such that TEXT_COLOR(255,0,0,255) would expand to "\x81\xFF\x00\x00\xFF" for use in constant strings?

You can certainly do it with TEXT_COLOR(FF,00,00,FF)

user3386109
– user3386109

2021-03-14 00:06:46 +00:00
Commented Mar 14, 2021 at 0:06 — user3386109
– user3386109, Commented Mar 14, 2021 at 0:06

Shawn · Accepted Answer · 2021-03-14 00:30:36Z

2

It takes a mix of token pasting and stringification in different macros, but, yeah, it's possible using base-16 numbers:

#include <stdio.h>

#define TEXT_COLOR2(r,g,b,a) "\x81" #r #g #b #a
#define TEXT_COLOR(r,g,b,a) TEXT_COLOR2(\x ##r, \x ##g, \x ##b, \x ##a)

int main(void) {
  char s[] = "Red text:" TEXT_COLOR(FF, 00, 00, FF) "hello!";
  for (const char *c = s; c < s + sizeof(s); c++) {
    printf("\\x%02hhX", *c);
  }
  putchar('\n');
  return 0;
}

answered Mar 14, 2021 at 0:30

Shawn

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