编译原理记忆dm

编译原理记忆dm

语法树结构

1 算术表达式

typedef enum { Plus, Minus, Times } OpKind;

typedef enum { Opkind, ConstKind } ExpKind;

typedef struct streenode {

	ExpKind kind;

	OpKind op;

	struct streenode *lchild, *rchild;

	int val;

} STreeNode;

typedef STreeNode* SynataxTree;

2 if语句：

typedef enum { ExpK, StmtK } NodeKind;

typedef enum { Zero, One } ExpKind;

typedef enum { IfK, OtherK } StmtKind;

typedef struct streenode {

	NodeKind kind;

	ExpKind ekind;

	struct streenode *test, *thenpart, *elsepart;

} STreeNode;

typedef STreeNode* SynataxTree;

递归子程序

1 match函数：

void match ( expectedToken )

{

	if (token==expectedToken)

	getToken( ); //获取下一个符号

	else Error( ); // 产生出错信息

} // match

2 Error函数

void Error ( int ErrorNo )

{

	switch(ErrorNo) {

		case 1: cout<<"漏了一个a或b" ;break;

		case 2: cout<<"漏了一个c或d";break;

		case 3: cout<<"漏了一个e或f";break;

		......

	}// switch

} //Error

3 实现算术表达式值的计算

//exp → exp + term | exp - term |term  =>  exp → term { (+|- ) term }

//每个递归函数返回当前计算结果

int exp( )

{

	int temp;

	temp = term( );

	while ((token =='+')||(token =='-') {

		switch (token ){

			case '+' :match ('+') ;
					  
					  temp = temp + term( );

      				  break;

			case '-': match ('-') ;

     			      temp = temp – term( );

   	 				  break;

		} //switch

	} while

	return temp ;

} //exp

4 算术表达式对应语法树的构造

//exp → term { (+|- ) term }

BTreeNode * exp( )

{

	BTreeNode * temp, *newtemp;

	temp = term( ) ;

	while ( token == '+' || token == '-' ) {

		newtemp = new BTreeNode ;

		newtemp ->data= token ;

		match (token) ;

		newtemp->lchild = temp ;

		newtemp->rchild= term( ) ;

		temp = newtemp ;

	}

	return temp ;

}// exp

5 为if语句构造相应的语法树

//if-stmt→if(exp)statement[else statement ]

syntaxTree ifStatement( )

{

	syntaxTree temp;

	match ("if") ;

	match ('(') ;

	temp =makeStmtNode(if) ; //生成新结点

	temp->testChild = exp( ) ;

	match (')' ) ;

	temp->thenChild = statement( ) ;

	if (token == "else" ) {

		match ("else") ;

		temp->elseChild = statement( ) ;

	}

	else temp->elseChild = NULL ;

} // ifStatement ;

6 求first集

void grammerTable::get_first(char target) {

	int tag = 0;

	int flag = 0;

	for (int i = 0; i<T; i++)

	{

		if (graStack[i].left == target)//匹配产生式左部

		{

			if (!isNotSymbol(graStack[i].right[0]) && graStack[i].right[0] != '*')//对于终结符，直接加入first

			{

				first_set[get_nindex(target)].insert(graStack[i].right[0]);

			}

			else

			{

				int j;

				if(graStack[i].right[0] == '*') //若为消除左递归后的结果则跳过'*'

					j = 1;

				else
					j = 0;

				for (; j<graStack[i].right.length(); j++) {

					if (!isNotSymbol(graStack[i].right[j]))//是终结符则结束

					{

						first_set[get_nindex(target)].insert(graStack[i].right[j]);

						break;

					}

					get_first(graStack[i].right[j]);//递归

					set<char>::iterator it;

					for (it = first_set[get_nindex(graStack[i].right[j])].begin();it != first_set[get_nindex(graStack[i].right[j])].end(); it++) 
					
					{

						if (*it == '#') flag = 1;

						else first_set[get_nindex(target)].insert(*it);//将FIRST(Y)中的非#就加入FIRST(X)

					}

					if (flag == 0) break;

					else {

						tag += flag;

						flag = 0;

					}

				}

				if (tag == graStack[i].right.length())//所有右部first(Y)都有#,将#加入FIRST(X)中

				first_set[get_nindex(target)].insert('#');

			}

		}

	}

}

7 求follow集

void grammerTable::get_follow(char target) {

	for (int i = 0; i<T; i++)

	{

		int index = -1;

		int len = int ( graStack[i].right.length());

		for (int j = 0; j<len; j++)

		{

			if (graStack[i].right[j] == target)

			{

				index = j;

				break;

			}

		}

		if (index != -1 && index < len - 1)

		{

			char nxt = graStack[i].right[index + 1];

			if (!isNotSymbol(nxt))

			{

				follow_set[get_nindex(target)].insert(nxt);

			}

			else

			{

				int isExt = 0;

				set<char>::iterator it;

				for (it = first_set[get_nindex(nxt)].begin(); it != first_set[get_nindex(nxt)].end(); it++)

				{

					if (*it == '#')

						isExt = 1;

					else

						follow_set[get_nindex(target)].insert(*it);

				}

				if (isExt && graStack[i].left != target)

				{

					get_follow(graStack[i].left);

					set<char>::iterator it;

					char tmp = graStack[i].left;

					for (it = follow_set[get_nindex(tmp)].begin(); it != follow_set[get_nindex(tmp)].end(); it++)

					{

						follow_set[get_nindex(target)].insert(*it);

					}

				}

			}

			else if (index != -1 && index == len - 1 && target != graStack[i].left)

			{

				get_follow(graStack[i].left);

				set<char>::iterator it;

				char tmp = graStack[i].left;

				for (it = follow_set[get_nindex(tmp)].begin(); it != follow_set[get_nindex(tmp)].end(); it++)

					follow_set[get_nindex(target)].insert(*it);

			}

		}

}