strlen_utf8_c.h

// UTF-8 is a variable-width encoding, with each character represented by one to four bytes, and for each UTF character, all // its non-first byte are start with 10xxxxxx, so the number of UTF characters could be counted by count the bytes that not 
// start with 10xxxxxx, and here comes the algorithrm
// http://en.wikipedia.org/wiki/UTF-8#Design

int strlen_utf8_c(char *s) {
  int i = 0, j = 0;
  while (s[i]) {
    if ((s[i] & 0xc0) != 0x80) j++;
    i++;
  }
  return j;
}