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bug in the compiler??

Alexander Sorockin

Hi All,

I don't believe this is actually a bug, but can anybody explain why this code works correctly

void func(int v1, int v2){
	unsigned char code tbl[] = {'a', 'b', 'c', 'd', 0, '1', '2', '3', '4'};
	signed char xdata diff = v1 - v2;

	if (diff >= -4 && diff <= 4)
		printf("%c\n", tbl[diff + 4]);

}
and this doesn't?
void func(int v1, int v2){
	unsigned char code tbl[] = {'a', 'b', 'c', 'd', 0, '1', '2', '3', '4'};
	int xdata diff = v1 - v2;

	if (diff >= -4 && diff <= 4)
		printf("%c\n", tbl[diff + 4]);

}
Is this behaviour ANSI-compliant?

Cheers

Parents
  • 0 in reply to Drew Davis

    I know what a "character" is, but I've always wondered what a negative signed char would be.

    Just a negative number in a small datatype (8-byte in C51, may be larger elsewhere). It's usually a good idea to think of all actual characters (i.e. the things written in 'a' notation) as unsgined values. That's what the C library does, too: see the description of <ctype.h> as an example.

Reply
  • 0 in reply to Drew Davis

    I know what a "character" is, but I've always wondered what a negative signed char would be.

    Just a negative number in a small datatype (8-byte in C51, may be larger elsewhere). It's usually a good idea to think of all actual characters (i.e. the things written in 'a' notation) as unsgined values. That's what the C library does, too: see the description of <ctype.h> as an example.

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