C / C ++十六进制char *到字节数组

Question

I've been trying to work out how to do this in embedded C++ for a while now, I've got a hex colour for a website in RGB888 eg "#ba00ff" that I want to convert into a C++ RGB555 hex value, eg 0x177C

Currently i've trimmed the # from the string and am stuck at converting it into a type I can use for creating the RGB555

my code currently looks like

 p_led_struct->color = "#ba00ff";
 char hexString[7] = {};
 memmove(hexString, p_led_struct->color+1, strlen(p_led_struct->color));
 byte colorBytes[3];
 sscanf(hexString,"%x%x%x",&colorBytes);

the hexString value becomes "ba00ff" correctly although the colorBytes array has incorrect data.

any assistance on how I should do this conversion would be awesome :)

Thanks!

Answer 1

Problems with sscanf(hexString,"%x%x%x",&colorBytes); are:

1. sscanf expects you to give 3 int s as a parameter but only one array is given and it is not int .
2. Single %x reads more than 2 characters.

Try:

int r, g, b;
if(sscanf(hexString,"%2x%2x%2x", &r, &g, &b) != 3) {
     // error
}

Edit:

Very useful info on scanf-family: http://en.cppreference.com/w/c/io/fscanf

Answer 2

Convert p_led_struct->color to an integer

p_led_struct->color = "#ba00ff";
unsigned int colorValue = strtoul(p_led_struct->color+1, NULL, 16);

and convert this RGB value into RGB555. The RGB integer has fields 0000.0000.rrrr.rrrr.gggg.gggg.bbbb.bbbb, and RGB555 has fields 0rrr.rrgg.gggb.bbbb, so we need only bit shifting:

unsigned short rgb555 = ((colorValue & 0x00f80000) >> 9) +  // red
  ((colorValue & 0x0000f800) >> 7) +  // green
  ((colorValue & 0x000000f8) >> 3);  // blue

Answer 3

Use hh modifier to scan directly into 1 byte.

p_led_struct->color = "#ba00ff";
byte colorBytes[3];
int result;
result = sscanf( p_led_struct->color, "#%2hhx%2hhx%2hhx", &colorBytes[0], 
    &colorBytes[1], &colorBytes[2]);
if (result != 3) {
  ; // handle problem
}

After you successfully scan the 3 RGB 8-bit bytes, recalculate the 3x5bit result.

int r,g,b;
r = colorBytes[0] >> 3;
g = colorBytes[1] >> 3;
b = colorBytes[2] >> 3;
printf("%04X", (r << 10) | (g << 5) | (b << 0));