C++中可正确获取UTF-8字符长度的函数分享_C/C++

C++中可正确获取UTF-8字符长度的函数分享

2021-01-25 14:31C++教程网 C/C++

这篇文章主要介绍了C++中可正确获取UTF-8字符长度的函数分享,需要的朋友可以参考下

在C++的char*以及string中，使用的是字节流编码，即sizeof(char) == 1。

也就是说，C++是不区分字符的编码的。

而一个合法UTF8的字符长度可能为1～4位。

现在假设一串输入为UTF8编码，如何能准确的定位到每个UTF8字符的“CharPoint”，而不会错误的分割字符呢？

参考这个页面：http://www.nubaria.com/en/blog/?p=289

可以改造出下面的函数：

									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;

									}