'comparison is always true due to limited range of data type' warning in C?

Question

I have the following code

//Point.h
#define WIDTH 8
#define HEIGHT 8

typedef struct Point
{
  char x;
  char y;
} Point;

//Board.c
#include <stdbool.h>

// Some other functions that we don't care about... 

bool inBounds(Point * p)
{
  return p->x >= 0
    && p->x <= WIDTH
    && p->y >= 0
    && p->y <= HEIGHT;
}

When I compile this (ppu-gcc 4.1.1), I get the following warning

warning: comparison is always true due to limited range of data type

even though the range of char is -127 to 127 and WIDTH is 8, which is well inside the range of a char. I've already tried an explicit cast of WIDTH to a char, but still got the error.

Answer 1

Are you sure that char is signed? Try declaring the fields explictly as signed char and see what you get.