UTF-8, Unicode, GB2312格式串转换之C语言版

来源:http://www.study-code.com/visual-studio/c/72913.htm

(申明:此文章属于原创,若转载请表明作者和原处链接 )      
      /*      author:   wu.jian   (吴剑)      English name: Sword
      /*      date:      2007-12-13
      /*      purpose:   知识共享



      这几天工作上碰到了UTF-8转GB2312的问题,而且是在嵌入式的环境下,没有API可用,查了很多网上的资料,大多调用VC或者linux下自带的接口。在这里我将这两天的工作做个总结。
      总的来说分为两大步(这里就不介绍基础知识了):

      一、UTF8 -> Unicode
      由于UTF8和Unicode存在着联系,所以不需要任何库就可以直接进行转换。首先要看懂UTF8的编码格式:
      U-00000000 - U-0000007F: 0xxxxxxx  
      U-00000080 - U-000007FF: 110xxxxx 10xxxxxx  
      U-00000800 - U-0000FFFF: 1110xxxx 10xxxxxx 10xxxxxx  
      U-00010000 - U-001FFFFF: 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx  
      U-00200000 - U-03FFFFFF: 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx  
      U-04000000 - U-7FFFFFFF: 1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx  
      前面几个1就代表后面几个字节是属于一起的。如果要解析一长串UTF8格式的字符串,这点就很有用了。下面这个函数就是判断前面几个1的(这里有define APP_PRINT printf,这样当release的时候将这个宏定义为空就行了,不需要一个一个去改,又方便重新调试):
      int GetUtf8ByteNumForWord(u8 firstCh)
      {
          u8 temp = 0x80;
          int num = 0;
 
          while (temp & firstCh)
          {
                num++;
                 temp = (temp >> 1);
           }

       APP_PRINT("the num is: %d", num);
        return num;
      }
      利用这个函数可以得到字符串中那几个字节是一起的。因为UTF8最大只有6个字节,所以就根据返回值来处理这里我只处理了3个字节和1个字节的UTF8的编码,因为一般来说中文在UTF8中是3个字节。

//将len个字节的UTF8格式的转换成GB2312格式存放在temp预先申请好的缓冲区中
void Utf8ToGb2312(const char* utf8, int len, char *temp)
{
       APP_PRINT("utf8->unicode: \n");
       APP_PRINT("utf8: [");
       for (int k = 0; k < len; k++)
       {
              APP_PRINT("%02x ", utf8[k]);
       }
       APP_PRINT("]\n");
 
       int byteCount = 0;
       int i = 0;
       int j = 0;

       u16 unicodeKey = 0;
       u16 gbKey = 0;


      //循环解析
       while (i < len)
       {   
        switch(GetUtf8ByteNumForWord((u8)utf8[i]))
        {
          case 0:
                temp[j] = utf8[i];
                byteCount = 1;
          break;

          case 2:
          temp[j] = utf8[i];
          temp[j + 1] = utf8[i + 1];
          byteCount = 2;
          break;

         case 3:
                 //这里就开始进行UTF8->Unicode
                 temp[j + 1] = ((utf8[i] & 0x0F) << 4) | ((utf8[i + 1] >> 2) & 0x0F);
                 temp[j] = ((utf8[i + 1] & 0x03) << 6) + (utf8[i + 2] & 0x3F);

                //取得Unicode的值
                 memcpy(&unicodeKey, (temp + j), 2);
                 APP_PRINT("unicode key is: 0x%04X\n", unicodeKey);

                  //根据这个值查表取得对应的GB2312的值
                gbKey = SearchCodeTable(unicodeKey);
                APP_PRINT("gb2312 key is: 0x%04X\n", gbKey);
    
                if (gbKey != 0)
                {
                       //here change the byte
                        //不为0表示搜索到,将高低两个字节调换调成我要的形式
                       gbKey = (gbKey >> 8) | (gbKey << 8);
                       APP_PRINT("after changing, gb2312 key is: 0x%04X\n", gbKey);
                       memcpy((temp + j), &gbKey, 2);
                  }

                byteCount = 3;
          break;

          case 4:
          byteCount = 4;
          break;
         case 5:
          byteCount = 5;
          break;
         case 6:
          byteCount = 6;
          break;
    
         default:
          APP_PRINT("the len is more than 6\n");
          break;    
        }

        i += byteCount;
        if (byteCount == 1)
        {
               j++;
        }
        else
        {
               j += 2;
        }
  
       }
       APP_PRINT("utf8: [");
       for (k = 0; k < j; k++)
       {
              APP_PRINT("%02x ", temp[k]);
       }
       APP_PRINT("]\n");
}

      二、下面主要谈谈利用查表法来进行Unicode->GB2312的转换,首先下载码表,一般码表都是将GB2312的放在前面,Unicode放在后面,这样对于我们来说不方便使用,所以我转换了下,将Unicode放在前面,而且按照从小到大排好序。(这里只需要考虑都为两个字节的情况,因为前面的UTF8->Unicode并没有将单字节的ASCII转换成Unicode)
            (1)做表:(可以到这里下载:http://blog.91bs.com/?action=show&id=20,这里谢谢渣渣的猪窝)
            这个是原来的样子:
            0x8140 0x4E02 #CJK UNIFIED IDEOGRAPH
            0x8141 0x4E04 #CJK UNIFIED IDEOGRAPH
            0x8142 0x4E05 #CJK UNIFIED IDEOGRAPH
            先弄成(这个可以写个小程序来做,我就是在VC上做的,如果需要可以联系我):
            { 0x4E02 ,0x8140 }, //CJK UNIFIED IDEOGRAPH
            { 0x4E04 ,0x8141 }, //CJK UNIFIED IDEOGRAPH
            { 0x4E05 ,0x8142 }, //CJK UNIFIED IDEOGRAPH
            这样就可以把这些放在.h文件中了,下面是我的定义:
            typedef struct unicode_gb
            {
                   unsigned short unicode;
                   unsigned short gb;
            } UNICODE_GB;

            UNICODE_GB code_table[] = 
            {
                  { 0x4E02, 0x8140 },   //CJK UNIFIED IDEOGRAPH
                  { 0x4E04, 0x8141 },  //CJK UNIFIED IDEOGRAPH
                  { 0x4E05, 0x8142 },  //CJK UNIFIED IDEOGRAPH
                  。。。。。。省略

            下面这一步也很简单,在VC中用冒泡排序法对整个表进行排序,这里是按照unicode值进行排序,把排序后的最终结果打印出来,在cmd下运行name > 1.txt就输出到文件,这样就有了一个按照unicode排好序的unicode->gb2312码表。以下是源代码:

   int main(int argc, char *argv[])
{

    int num = 0;
    UNICODE_GB temp;
    int i = 0;
    int j = 0;

    num = sizeof(code_table) / sizeof(UNICODE_GB);

    printf("struct size: %d | total size: %d | num is: %d \n", 
    sizeof(UNICODE_GB), sizeof(code_table), num);

    for (i = 0; i < num; i++)
    {
        for (j = 1; j < num - i; j++)
        {
            if (code_table[j - 1].unicode > code_table[j].unicode)
            {
                temp.unicode = code_table[j - 1].unicode;
                temp.gb = code_table[j - 1].gb;
                code_table[j - 1].unicode = code_table[j].unicode;
                code_table[j - 1].gb = code_table[j].gb;
                code_table[j].unicode = temp.unicode;
                code_table[j].gb = temp.gb;
            }
        }
    }

    printf("here is the code table sorted by unicode\n\n");

    for (i = 0; i < num; i++)
    {
        printf("{\t0x%04X,\t0x%04X\t},\t\n", code_table[i].unicode, code_table[i].gb);
     }

       printf("\n\n print over!\n");

   //以下注释掉的其实就是我用来对原来的码表添加,{,}等用的
   /*
    char buff[100];
    char buff_1[100]; 
 
    FILE* fp = NULL;
    FILE *fp_1 = NULL;

    memset(buff, 0, 100);
    memset(buff_1, 0, 100);
 
    fp = fopen("table.txt", "rw");
    fp_1 = fopen("table_1.txt", "a+");

    if ((fp == NULL) || (fp_1 == NULL))
    {
        printf("open file error!\n");
        return 1;
    }

    while (fgets(buff, 100, fp) != NULL)
    {
        buff[8] = ',';

        fputs(buff, fp_1);
    }
 */

    return 0;
}

      最后就是搜索算法了,前面已经排好序了,现在我们把排好序的码表放在我们真正需要的.h文件中。大家应该猜我用什么算法搜索了吧,二分法。

#define CODE_TABLE_SIZE 21791
//这个表是死的,所以就直接用宏表示长度,不用每次都用size,不过这样可能对移植性不好。
u16 SearchCodeTable(u16 unicodeKey)
{
    int first = 0;
    int end = CODE_TABLE_SIZE - 1;
    int mid = 0;

    while (first <= end)
    {
        mid = (first + end) / 2;

        if (code_table[mid].unicode == unicodeKey)
        {
            return code_table[mid].gb;
        }
        else if (code_table[mid].unicode > unicodeKey)
        {
            end = mid - 1;
        }
        else 
        {
            first = mid + 1;
        }
    }
    return 0;
}
      到此,已经能够将UTF8串转换成GB2312了。是一长串哦,而不是单个汉字的编码转换。 

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