C++中可正确获取UTF-8字符长度的函数分享

const unsigned char kFirstBitMask = 128; // 1000000
const unsigned char kSecondBitMask = 64; // 0100000
const unsigned char kThirdBitMask = 32; // 0010000
const unsigned char kFourthBitMask = 16; // 0001000
const unsigned char kFifthBitMask = 8; // 0000100
 
int utf8_char_len(char firstByte)
{
  std::string::difference_type offset = 1;

  if(firstByte & kFirstBitMask) // This means the first byte has a value greater than 127, and so is beyond the ASCII range.
  {  
    if(firstByte & kThirdBitMask) // This means that the first byte has a value greater than 224, and so it must be at least a three-octet code point.
    {  
      if(firstByte & kFourthBitMask) // This means that the first byte has a value greater than 240, and so it must be a four-octet code point.
        offset = 4;
      else
        offset = 3;
    }  
    else
    {  
      offset = 2;
    }  
  }  
  return offset;
}