UTF8编码格式的中英文字符如何换行

/*
功能：UTF8中英文字符换行
输入：szStr: 字符串
      ncount：每行容纳的中文字符
输出：lineStr: 每一行字符
返回：无
*/

static void philofly_break_line(char *szStr, int ncount, char **lineStr)
{
    int nsum = 0;
    int ntotal  = ncount*3;
    int i = 0;

    if(szStr == NULL || lineStr == NULL || *lineStr == NULL)
        return;
    
    
    if(strlen(szStr) < ntotal)
    {
         strcpy(*lineStr, szStr);
         return;
    }
    
    while( *szStr)
    {
        if( (*szStr) < 0)//chinese char
        {
           nsum += 3;
           szStr += 3;
        }
        else// 'a' to 'z' or 'A' to 'Z' or '0' to '9'
        {
           szStr++;
           nsum++;
        }
        if(nsum>=ntotal || (*szStr=='\0') )
        {
             if( *szStr == '\0 )
             {
                 strncpy(lineStr[i], szStr-nsum, nsum);//last chars
                 break;
             }
             if(nsum==ntotal)
             {
                strncpy(lineStr[i], szStr-nsum, ntotal);
             }
             else if(nsum > ntotal)
             {
                if(nsum%3 == 1)// more one digital or english char 
                {
                   strncpy(lineStr[i], szStr-nsum, ntotal-1);
                   szStr -= 1;

                }
                else if(nsum%3 == 2)//more one chinese char
                {
                   strncpy(lineStr[i], szStr-nsum, ntotal-3);
                   szStr -= 3;

                }
            }
        }
        nsum = 0;
        i++;
    }
 }