[源码试]写xml的解析器

写了一个对xml文件的词法分析,程序的分析引擎用switch+state写的,主要是为加深对词法分析的理解.

 while (sr.Peek()!=-1)
            {
                //int c = sr.Read();
                //Char ch = (char)c;
                //Console.WriteLine("{0}\t {1}\t {2}",ch,c, Convert.ToString(c,2).PadLeft(16,'0') );
                /**/////switch
                c = (char)sr.Read();
                switch(state)
                {
                    case 0://普通
                        jumpspace();
                        if(c=='<')
                            state = 10;
                        break;
                    case 10://<[?]
                        switch(c)
                        {
                            case '?': state =11;//<? 
                                break;
                            case ' ':
                            case '\t':
                            case '\r':
                            case '\n':
                                throw new Exception("该位置上不允许有空白");
                                break;
                            case '/':
                                state = 50;//结束<[/].>
                                break;
                            default:
                                state = 20;//元素名
                                sb.Remove(0,sb.Length);//加元素
                                sb.Append(c);

                                while (sr.Peek() != -1)
                                {
                                    char nextchar = (char)sr.Peek();
                                    if (char.IsLetter(nextchar))
                                    {
                                        sb.Append(nextchar);//element
                                        c = (char)sr.Read();
                                    }
                                    else
                                    {
                                        //完成元素
                                        //string temp = sb.ToString();
                                        Console.WriteLine(sb.ToString());
                                        StID.Push(sb.ToString());
                                        sb.Remove(0, sb.Length);

                                        state = 15;//后接 /  > ' '
                                        jumpspace();
                                        break;
                                    }
                                }
                                break;
                        }
                        break;
                    case 11://<?[x]  --系统
                        switch(c)
                        {
                            case 'x':
                                state =12;
                                break;                                
                        }
                        break;
                    case 15:
                        jumpspace();
                        if (c == '/' )
                        {
                            Console.WriteLine( StID.Pop());
                            //完成
                            c =(char)sr.Read();
                            if (c != '>')
                                throw new Exception("/>");

                            //下来可能是节点,也可能是文本
                            state = 0;
                        }
                        else if (c == '>')
                        {
                            state = 0;//原始状态
                        }

                        else if (char.IsLetterOrDigit(c))
                        {
                            //sb.Append(c);//属性
                            //属性开始
                            state = 30;
                            goto case 30;
                        }
                        else
                        {
                            throw new Exception("错误的属性");
                        }
                        
                        break;
                    case 20://元素名-第二个 只是元素
                        if (char.IsLetterOrDigit(c))
                        {
                            sb.Append(c);//element
                        }
                        else if (char.IsWhiteSpace(c))//遍历空白
                        {
                            //完成
                            //string temp = sb.ToString();
                            Console.WriteLine(sb.ToString());
                            StID.Push(sb.ToString());
                            sb.Remove(0, sb.Length);
                            while (true)
                            {
                                c = (char)sr.Peek();
                                if (!char.IsWhiteSpace(c))//如果不空白,跳出
                                    break;
                                sr.Read();
                            }
                            state = 30;//属性
                        }
                        else if (c == '>')
                        {
                            //完成
                            //string temp = sb.ToString();
                            Console.WriteLine(sb.ToString());
                            StID.Push(sb.ToString());
                            sb.Remove(0, sb.Length);
                            state = 15;//中间状态,下一个可能是元素也可能是text
                        }
                        else
                        {
                            throw new Exception("无效的字符");
                        }                        
                        break;

                    case 30://属性名first 后继
                        if (char.IsLetterOrDigit(c))
                        {
                            sb.Append(c);//属性
                        }     
                        else
                        {
                            goto case 31;
                        }
                        break;
                    case 31:
                        jumpspace();
                        if(c=='=')
                        {
                            state =32;
                            
                        }                        
                        else
                        {
                            throw new Exception("属性无效字符!");
                        }
                        break;
                    case 32://属性引号
                        jumpspace();                        
                        switch(c)
                        {
                            case '\'':
                                state =36;//单引号;
                                break;
                            case '\"':
                                state = 37;//双引号
                                break;
                            default:
                                throw new Exception("应该是引号");

                        }
                        
                        break;
                    case 36:
                        
                        switch (c)
                        {
                            case '\'':
                                state = 30;//复原,下一属性
                                jumpspace();
                                state = 15;
                                break;   
                            case '>':
                                throw new Exception("没有结束引号");
                                break;
                        }
                        break;
                    case 37:
                        switch (c)
                        {
                            case '\"':
                                state = 30;//复原,下一属性
                                jumpspace();
                                state = 15;
                                break;
                            case '>':
                                throw new Exception("没有结束引号");
                                break;
                        }
                        break;
                    case 50:
                        sb.Remove(0,sb.Length);
                        if (char.IsLetterOrDigit(c))
                            sb.Append(c);
                        else
                            throw new Exception("错误的结束字符");

                        while (sr.Peek() != -1)
                        {
                            tempc = (char)sr.Peek();
                            if (char.IsLetterOrDigit(tempc))
                            {
                                sb.Append(tempc);
                                c = (char)sr.Read();
                            }
                            else
                            {
                                //Console.WriteLine(StID.Peek
                                tempstr = StID.Peek();
                                if(StID.Pop()!=sb.ToString())
                                    throw new Exception (string.Format( "结束标记 '{0}' 与开始标记 '{1}' 不匹配"
                                        ,sb.ToString()
                                        ,tempstr));
                                state =51;//处理结尾 ' ' >
                                break;
                            }
                            
                        }
                        break;
                    case 51:
                        jumpspace();
                        switch (c)
                        {
                            case '>':
                                state = 0;//普通状态
                                break;
                            default:
                                throw new Exception("名称包含无效字符");
                        }
                        break;
                        

 

                }

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