functions not calling correctly

I'm writing a program that takes a color number (1-7) and prints out it's respective RGB. I created a function that takes the color and sets its RGB values then returns it back to the function. For some reason the r, g, and b ints aren't returning back and printing out correctly. Any ideas???
Thanks in advance!

Quote:

---

if (InObject(shapeLetter, newX, newY, arg1, arg2, arg3)){
Rectangle(arg1, arg2, newX, newY);
printPix(color, r, g, b);
newR = r;
newG = g;
newB = b;
}
printf("%d %d %d # %d %d\n", newR, newG, newB, x, y);
}
}

int printPix(int color, int r, int g, int b) {
if (color == 0){
r = 0; g = 0; b = 0;
}
else if (color == 1){
r = MAX_COLOR; g = 0; b = 0;
}
else if (color == 2){
r = 0; g = MAX_COLOR; b = 0;
}
else if (color == 3){
r = 0; g = 0; b = MAX_COLOR;
}
else if (color == 4){
r = 0; g = MAX_COLOR; b = MAX_COLOR;
}
else if (color == 5){
r = MAX_COLOR; g = 0; b = MAX_COLOR;
}
else if (color == 6){
r = MAX_COLOR; g =MAX_COLOR ; b = 0;
}
else if (color == 7){
r = MAX_COLOR; g = MAX_COLOR; b = MAX_COLOR;
}
return;
}

---

Well... mostly it's because your function isn't returning anything of value. In fact you should be getting compiler warnings about it not returning a value...

Then there's the little problem that a C program can only return 1 value... not three.

If you want to return more than one value you need to pass in a pointer to the variables that are to be changed and operate on the pointers...

Code:

---

void PrintPix(int color, int *r, int *g, int *b)
  { if (color == 0){r = 0; g = 0; b = 0;}
    else if (color == 1){*r = MAX_COLOR; *g = 0; *b = 0;}
    else if (color == 2){*r = 0; *g = MAX_COLOR; *b = 0;}
    else if (color == 3){*r = 0; *g = 0; *b = MAX_COLOR;}
    else if (color == 4){*r = 0; *g = MAX_COLOR; *b = MAX_COLOR;}
    else if (color == 5){*r = MAX_COLOR; *g = 0; *b = MAX_COLOR;}
    else if (color == 6){*r = MAX_COLOR; *g =MAX_COLOR ; *b = 0;}
    else if (color == 7){*r = MAX_COLOR; *g = MAX_COLOR; *b = MAX_COLOR;} }



// call it as...
PrintPix(color,&r,&g,&b);

---

I would just like to point out that it is much more common have color as a structure. E.g.

Code:

---

#include <stdio.h>


typedef struct color
{
  int red, green, blue;
} ColorRGB;

ColorRGB make_rgb(int R, int G, int B);


int main(void)
{
  ColorRGB orange;
  orange = make_rgb(255, 127, 0);
 
  return 0;
}


ColorRGB make_rgb(int R, int G, int B)
{
  ColorRGB C;
 
  C.red = R;
  C.green = G;
  C.blue = B;
 
  return C;
}

---

Just an example.

I would use a switch statement in teh function instead of a battery of else-if constructs.

Actually, a common solution to this is not to make a function at all, but a constant map. It's faster, but you have to take care not to go out of bounds on the color index.

Code:

---

/* in your headers, use */
#define MAX_COLOR 255

typedef struct _rgbcolor {
  int r,g,b;
} rgbcolor_t;

rgbcolor_t colormap[]= {
  { 0, 0, 0 },
  { MAX_COLOR, 0, 0 },
  { 0, MAX_COLOR, 0 },
  { 0, 0, MAX_COLOR },
  { 0, MAX_COLOR, MAX_COLOR },
  { MAX_COLOR, 0, MAX_COLOR },
  { 0, MAX_COLOR, MAX_COLOR},
  { MAX_COLOR, MAX_COLOR, MAX_COLOR }
};


/* in your code, use: */
int newR, newG, newB;

newR = colormap[color].r;
newG = colormap[color].g;
newB = colormap[color].b;

/* OR */
rgbcolor_t myRGB;

myRGB = colormap[color];

---

my 2 cents,
LT