C++中可准確獲得UTF-8字符長度的函數分享

C++中可准確獲得UTF-8字符長度的函數分享。本站提示廣大學習愛好者：（C++中可准確獲得UTF-8字符長度的函數分享）文章只能為提供參考，不一定能成為您想要的結果。以下是C++中可准確獲得UTF-8字符長度的函數分享正文

在C++的char*和string中，應用的是字撙節編碼，即sizeof(char) == 1。

也就是說，C++是不辨別字符的編碼的。

而一個正當UTF8的字符長度能夠為1～4位。

如今假定一串輸出為UTF8編碼，若何能精確的定位到每一個UTF8字符的“CharPoint”，而不會毛病的朋分字符呢？

參考這個頁面：http://www.nubaria.com/en/blog/?p=289

可以改革出上面的函數：

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;
}