test.c

char *strtrim(char *str)
{
	size_t len;
	char *pb;
	for (pb = str; isspace(*pb); pb++); /* isspace(0) == 0 */
	for (len = strlen(pb); len > 0 && isspace(pb[len - 1]); len--);
	if (pb > str && len > 0)
		memmove(str, pb, len);
	str[len] = 0;
	return str;
}

char *strtrim2(char *str)
{
	char c = 0;
	char *pb = str, *pe = str, *p = str;
	while ((c = *p++)) {
		if (isspace(c) && pb == str)
			continue;
		*pb++ = c;
		if (!isspace(c)) pe = pb;
	}
	*pe = 0;

	return str;
}