Question

我在C中有一个char *字符串，它基于用户输入。从这个字符串开始，我想从第一个位置开始选择一个子串，这样得到的子串在固定宽度的终端上是n列宽。

过去从未使用过非ASCII字符，我完全不知道如何处理这个问题，甚至开始。一些初步搜索建议使用libiconv，但似乎没有帮助。我也尝试使用wchar.h，广泛的角色支持，但我不确定这是正确的方法。

编辑：这是我在第一次尝试中尝试的内容：

static int
count_n_cols (const char *mbs, char *mbf, const int n)
{
  wchar_t wc;
  int     bytes;
  int     remaining = strlen(mbs);
  int     cols = 0;
  int     wccols;

  while (*mbs != '\0' && cols <= n)
    {
      bytes = mbtowc (&wc, mbs, remaining);
      assert (bytes != 0);  /* Only happens when *mbs == '\0' */
      if (bytes == -1)
        {
          /* Invalid sequence. We'll just have to fudge it. */
          return cols + remaining;
        }
      mbs += bytes;
      remaining -= bytes;
      wccols = wcwidth(wc);
      *mbf += wc;
      cols += (wccols == -1? 1 : wccols);
    }
  return cols;
}

Answer 1

如果我正确理解了您的问题，您需要计算utf-8序列的数量来执行子字符串而不进行任何转换。您可以计算与每个列相对应的字节数＆＃39;通过读取序列的第一个字节，如utf-8标准所规定的那样。以下是一些示例代码，基于您的示例函数和Wikipedia's UTF-8 description：

static int count_n_cols (const char *mbs, char *mbf, const int n)
{
    int bytes;
    int length = strlen(mbs);
    int cols = 0;

    for (bytes = 0; bytes < length; bytes++)
    {
        if (mbs[bytes] == '\0' || cols >= n)
            break;
        else if ((mbs[bytes] & 0x80) == 0)  // the first bit is 0
        {
            cols++;
        }
        else if ((mbs[bytes] & 0xE0) == 0xC0)   //the first 3 bits are 110
        {
            //two bytes in utf8 sequence
            cols++;
            bytes++;
        }
        else if ((mbs[bytes] & 0xF0) == 0xE0)   //the first 4 bits are 1110
        {
            //three bytes in utf8 sequence
            cols++;
            bytes += 2;
        else if ((mbs[bytes] & 0xF8) == 0xF0)   //the first 5 bits are 11110
        {
            //four bytes in utf8 sequence
            cols++;
            bytes += 3;
        }
        else
        {
            putc(mbs[bytes],stdout);
            printf(" non_ascii %d\n", mbs[bytes] & 0x80);
        }
    }
    strncpy(mbf, mbs, bytes);
    mbf[bytes] = '\0';
    return cols;
}

C：从多字节字符串中选择一个子字符串，n列宽

1 个答案: