实验三--LR(1)分析法实验报告.doc

实验三 LR(1)分析法
一、实验目的
构造LR(1)分析程序，利用它进行语法分析，判断给出的符号串是否为该文法识别的句子，了解LR（K）分析方法是严格的从左向右扫描，和自底向上的语法分析方法。
二、LR（1）分析法实验设计思想及算法
(1)总控程序，也可以称为驱动程序。对所有的LR分析器总控程序都是相同的。
(2)分析表或分析函数，不同的文法分析表将不同，同一个文法采用的LR分析器不同时，分析表将不同，分析表又可以分为动作表（ACTION）和状态转换（GOTO）表两个部分，它们都可用二维数组表示。
(3)分析栈，包括文法符号栈和相应的状态栈，它们均是先进后出栈。
分析器的动作就是由栈顶状态和当前输入符号所决定。
u LR分析器由三个部分组成：

u 其中:SP为栈指针，S[i]为状态栈，X[i]为文法符号栈。状态转换表用GOTO[i，X]=j表示，规定当栈顶状态为i，遇到当前文法符号为X时应转向状态j，X为终结符或非终结符。
u ACTION[i，a]规定了栈顶状态为i时遇到输入符号a应执行。动作有四种可能：
(1)移进：
action[i，a]= Sj：状态j移入到状态栈，把a移入到文法符号栈，其中i,j表示状态号。
(2)归约：action[i，a]=rk：当在栈顶形成句柄时，则归约为相应的非终结符A，即文法中有A- B的产生式，若B的长度为R(即|B|=R)，则从状态栈和文法符号栈中自顶向下去掉R个符号，即栈指针SP减去R，并把A移入文法符号栈内，j=GOTO[i,A]移进状态栈，其中i为修改指针后的栈顶状态。
(3)接受acc:当归约到文法符号栈中只剩文法的开始符号S时，并且输入符号串已结束即当前输入符是'#'，则为分析成功。
(4)报错:当遇到状态栈顶为某一状态下出现不该遇到的文法符号时，则报错，说明输入端不是该文法能接受的符号串。

三、程序结构描述
1、定义的变量
string action[12][6]={
{"s5","error","error","s4","error","error"},
{"error","s6","error","error","error","acc"},
{"error","r2","s7","error","r2","r2"},
{"error","r4","r4","error","r4","r4"},
{"s5","error","error","s4","error","error"},
{"error","r6","r6","error","r6","r6"},
{"s5","error","error","s4","error","error"},
{"s5","error","error","s4","error","error"},
{"error","s6","error","error","s11","error"},
{"error","r1","r7","error","r1","r1"},
{"error","r3","r3","error","r3","r3"},
{"error","r5","r5","error","r5","r5"}
};

string go[12][3]={
{"1","2","3"},
{"error","error","error"},
{"error","error","error"},
{"error","error","error"},
{"8","2","3"},
{"error","error","error"},
{"error","9","3"},
{"error","error","10"},
{"error","error","error"},
{"error","error","error"},
{"error","error","error"},
{"error","error","error"},
}; //初始化预测分析表
char Vt[6]={'i','+','*','(',')','#'}; 终结符表
string LR[6]={"E->E+T","E->T","T->T*F","T->F","F->(E)","F->i"};//LR文法
stackS; 状态栈
stackX; 符号栈

char input[10]; 输入字符
2、定义的函数
int num(string s) 判断字符串中的数字
void print(int i,char*c) 剩余输入串的输出
int same(char a) 用于查找终结符
void analyse() 分析程序
四、程序源代码及运行结果
#include
#include
#include
#include
using namespace std;
//初始化预测分析表
string action[12][6]={
{"s5","error","error","s4","error","error"},
{"error","s6","error","error","error","acc"},
{"error","r2","s7","error","r2","r2"},
{"error","r4","r4","error","r4","r4"},
{"s5","error","error","s4","error","error"},
{"error","r6","r6","error","r6","r6"},
{"s5","error","error","s4","error","error"},
{"s5","error","error","s4","error","error"},
{"error","s6","error","error","s11","error"},
{"error","r1","r7","error","r1","r1"},
{"error","r3","r3","error","r3","r3"},
{"error","r5","r5","error","r5","r5"}
};

string go[12][3]={
{"1","2","3"},
{"error","error","error"},
{"error","error","error"},
{"error","error","error"},
{"8","2","3"},
{"error","error","error"},
{"error","9","3"},
{"error","error","10"},
{"error","error","error"},
{"error","error","error"},
{"error","error","error"},
{"error","error","error"},
};
char Vt[6]={'i','+','*','(',')','#'};//终结符表
string LR[6]={"E->E+T","E->T","T->T*F","T->F","F->(E)","F->i"};//LR文法
stackS; //状态栈
stackX; //符号栈
char input[10]; //输入字符
int num(string s){ //判断字符串中的数字
int i;
string str="";
for(int j=0;j='0'&&s[j]<='9') str=str+s[j];
}
i=atoi(str.c_str());
return i;
}
void print(int i,char*c)//剩余输入串的输出
{
for(int j=i;j<10;j++)
cout<oint=0,state=0; //步骤、指针、状态
char ch1,ch2;
int m,n,l; //用于判断终结符,分析表,表达式右部的长度
string str1; //用于判断对应分析表中的符号
string str2="#",str3="0"; //记录符号栈的所有元素
cout<<"请输入要规约的字符串："<>input;
X.push('#');
S.push(0);

cout<<"步骤"<<'\t'<<"状态栈"<<'\t'<<"符号栈"<<'\t'<<"输入串 "<<'\t'<<"动作"<移进动作
if(str1[0]=='s'){
n=num(str1);
S.push(n);
X.push(ch1);
str2=str2+ch1;
ch2=n+48;
str3=str3+ch2;
point++;
cout<)-3;

for(int i=1;i<=l;i++) {S.pop();
str3=str3.substr(0,str3.length()-1);

X.pop();
str2=str2.substr(0,str2.length()-1);
}

X.push(LR[n-1][0]);
str2=str2+LR[n-1][0];
state=S.top();
if(LR[n-1][0]=='E'){S.push(num(go[state][0]));
ch2=num(go[state][0])+48;
str3=str3+ch2;

}
else if(LR[n-1][0]=='T'){S.push(num(go[state][1]));
ch2=num(go[state][1])+48;
str3=str3+ch2;

}
else if(LR[n-1][0]=='F') {S.push(num(go[state][2]));
ch2=num(go[state][2])+48;
str3=str3+ch2;

}

cout<}
//*********出错
else if(str1=="error"){
cout<<"ERROR"<<"程序错误，分析结束！！！"<