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语法分析程序设计
【实验目的】
1.熟悉判断LL(1)文法的方法及对某一输入串的分析过程。
2.学会构造表达式文法的预测分析表。
【实验内容】
编写一个语法分析程序,对于给定的输入串,能够判断识别该串是否为给定文法的句型。
【实验要求】
1. 输入一个LL(1)文法,构造相应的LL(1)预测分析表。
2. 从键盘读入输入串,由算法判断该输入串是否为该文法的句子,若正确,就通过,若错误就报错。
【参考说明】
语法分析主要是将从词法分析那里得来的记号构成一棵语法树。例:
SHMA#adbe#
S->aH
H->aMd
H->d
M->Ab
M->
A->aM
A->e
【实验代码】
//LL1.h
#ifndef LL1_H_INCLUDED
#define LL1_H_INCLUDED
#include "stdio.h"
#include "stdlib.h"
#define MaxRuleNum 8
#define MaxVnNum 5
#define MaxVtNum 5
#define MaxStackDepth 20
#define MaxPLength 20
#define MaxStLength 50
struct pRNode /*产生式右部结构*/
{
int rCursor; /*右部序号*/
struct pRNode *next;
};
struct pNode /*产生式结点结构*/
{
int lCursor; /*左部符号序号*/
int rLength; /*右部长度*/
/*注当rLength = 1 时,rCursor = -1为空产生式*/
struct pRNode *rHead; /*右部结点头指针*/
};
char Vn[MaxVnNum + 1]; /*非终结符集*/
int vnNum;
char Vt[MaxVtNum + 1]; /*终结符集*/
int vtNum;
struct pNode P[MaxRuleNum]; /*产生式*/
int PNum; /*产生式实际个数*/
char buffer[MaxPLength + 1];
char ch; /*符号或string ch;*/
char st[MaxStLength]; /*要分析的符号串*/
struct collectNode /*集合元素结点结构*/
{
int nVt; /*在终结符集中的下标*/
struct collectNode *next;
};
struct collectNode* first[MaxVnNum + 1]; /*first集*/
struct collectNode* follow[MaxVnNum + 1]; /*follow集*/
int analyseTable[MaxVnNum + 1][MaxVtNum + 1 + 1];
/*预测分析表存放为产生式的编号,+1用于存放结束符,多+1用于存放#(-1)*/
int analyseStack[MaxStackDepth + 1]; /*分析栈*/
int topAnalyse; /*分析栈顶*/
/*int reverseStack[MaxStackDepth + 1]; /*颠倒顺序栈*/
/*int topReverse; /*倒叙栈顶*/
void Init();/*初始化*/
int IndexCh(char ch);
/*返回Vn在Vn表中的位置+100、Vt在Vt表中的位置,-1表示未找到*/
void InputVt(); /*输入终结符*/
void InputVn();/*输入非终结符*/
void ShowChArray(char* collect, int num);/*输出Vn或Vt的内容*/
void InputP();/*产生式输入*/
bool CheckP(char * st);/*判断产生式正确性*/
void First(int U);/*计算first集,U->xx...*/
void AddFirst(int U, int nCh); /*加入first集*/
bool HaveEmpty(int nVn); /*判断first集中是否有空(-1)*/
void Follow(int V);/*计算follow集*/
void AddFollow(int V, int nCh, int kind);/*加入follow集,
kind = 0表加入follow集,kind = 1加入first集*/
void ShowCollect(struct collectNode **collect);/*输出first或follow集*/
void FirstFollow();/*计算first和follow*/
void CreateAT();/*构造预测分析表*/
void ShowAT();/*输出分析表*/
void Identify(char *st);/*主控程序,为操作方便*/
/*分析过程显示操作为本行变换所用,与教程的显示方式不同*/
void InitStack();/*初始化栈及符号串*/
void ShowStack();/*显示符号栈中内容*/
void Pop();/*栈顶出栈*/
void Push(int r);/*使用产生式入栈操作*/
#endif // HEAD_H_INCLUDED
//main.cpp
#include "LL1.h"
int main(void)
{
char todo,ch;
Init();
InputVn();
InputVt();
InputP();
getchar();
FirstFollow();
printf("所得first集为:");
ShowCollect(first);
printf("所得follow集为:");
ShowCollect(follow);
CreateAT();
ShowAT();
todo = 'y';
while('y' == todo)
{
printf("\n是否继续进行句型分析?(y / n):");
todo = getchar();
while('y' != todo && 'n' != todo)
{
printf("\n(y / n)? ");
todo = getchar();
}
if('y' == todo)
{
int i;
InitStack();
printf("请输入符号串(以#结束) : ");
ch = getchar();
i = 0;
while('#' != ch && i < MaxStLength)
{
if(' ' != ch && '\n' != ch)
{
st[i++] = ch;
}
ch = getchar();
}
if('#' == ch && i < MaxStLength)
{
st[i] = ch;
Identify(st);
}
else
printf("输入出错!\n");
}
}
getchar();
}
void Init()
{
int i,j;
vnNum = 0;
vtNum = 0;
PNum = 0;
for(i = 0; i <= MaxVnNum; i++)
Vn[i] = '\0';
for(i = 0; i <= MaxVtNum; i++)
Vt[i] = '\0';
for(i = 0; i < MaxRuleNum; i++)
{
P[i].lCursor = NULL;
P[i].rHead = NULL;
P[i].rLength = 0;
}
PNum = 0;
for(i = 0; i <= MaxPLength; i++)
buffer[i] = '\0';
for(i = 0; i < MaxVnNum; i++)
{
first[i] = NULL;
follow[i] = NULL;
}
for(i = 0; i <= MaxVnNum; i++)
{
for(j = 0; j <= MaxVnNum + 1; j++)
analyseTable[i][j] = -1;
}
}
/*返回Vn在Vn表中的位置+100、Vt在Vt表中的位置,-1表示未找到*/
int IndexCh(char ch)
{
int n;
n = 0; /*is Vn?*/
while(ch != Vn[n] && '\0' != Vn[n])
n++;
if('\0' != Vn[n])
return 100 + n;
n = 0; /*is Vt?*/
while(ch != Vt[n] && '\0' != Vt[n])
n++;
if('\0' != Vt[n])
return n;
return -1;
}
/*输出Vn或Vt的内容*/
void ShowChArray(char* collect)
{
int k = 0;
while('\0' != collect[k])
{
printf(" %c ", collect[k++]);
}
printf("\n");
}
/*输入非终结符*/
void InputVn()
{
int inErr = 1;
int n,k;
char ch;
while(inErr)
{
printf("\n请输入所有的非终结符,注意:");
printf("请将开始符放在第一位,并以#号结束:\n");
ch = ' ';
n = 0;
/*初始化数组*/
while(n < MaxVnNum)
{
Vn[n++] = '\0';
}
n = 0;
while(('#' != ch) && (n < MaxVnNum))
{
if(' ' != ch && '\n' != ch && -1 == IndexCh(ch))
{
Vn[n++] = ch;
vnNum++;
}
ch = getchar();
}
Vn[n] = '#'; /*以“#”标志结束用于判断长度是否合法*/
k = n; /*k用于记录n以便改Vn[n]='\0'*/
if('#' != ch)
{
if( '#' != (ch = getchar()))
{
while('#' != (ch = getchar()))
;
printf("\n符号数目超过限制!\n");
inErr = 1;
continue;
}
}
/*正确性确认,正确则,执行下下面,否则重新输入*/
Vn[k] = '\0';
ShowChArray(Vn);
ch = ' ';
while('y' != ch && 'n' != ch)
{
if('\n' != ch)
{
printf("输入正确确认?(y/n):");
}
scanf("%c", &ch);
}
if('n' == ch)
{
printf("录入错误重新输入!\n");
inErr = 1;
}
else
{
inErr = 0;
}
}
}
/*输入终结符*/
void InputVt()
{
int inErr = 1;
int n,k;
char ch;
while(inErr)
{
printf("\n请输入所有的终结符,注意:");
printf("以#号结束:\n");
ch = ' ';
n = 0;
/*初始化数组*/
while(n < MaxVtNum)
{
Vt[n++] = '\0';
}
n = 0;
while(('#' != ch) && (n < MaxVtNum))
{
if(' '!= ch && '\n' != ch && -1 == IndexCh(ch))
{
Vt[n++] = ch;
vtNum++;
}
ch = getchar();
}
Vt[n] = '#'; /*以“#”标志结束*/
k = n; /*k用于记录n以便改Vt[n]='\0'*/
if('#' != ch)
{
if( '#' != (ch = getchar()))
{
while('#' != (ch = getchar()))
printf("\n符号数目超过限制!\n");
inErr = 1;
continue;
}
}
/*正确性确认,正确则,执行下下面,否则重新输入*/
Vt[k] = '\0';
ShowChArray(Vt);
ch =' ';
while('y' != ch && 'n' != ch)
{
if('\n' != ch)
{
printf("输入正确确认?(y/n):");
}
scanf("%c", &ch);
}
if('n' == ch)
{
printf("录入错误重新输入!\n");
inErr = 1;
}
else
{
inErr = 0;
}
}
}
/*产生式输入*/
void InputP()
{
char ch;
int i = 0, n,num;
printf("请输入文法产生式的个数:");
scanf("%d", &num);
PNum = num;
getchar(); /*消除回车符*/
printf("\n请输入文法的%d个产生式,并以回车分隔每个产生式:", num);
printf("\n");
while(i < num)
{
printf("第%d个:", i);
/*初始化*/
for(n =0; n < MaxPLength; n++)
buffer[n] = '\0';
/*输入产生式串*/
ch = ' ';
n = 0;
while('\n' != (ch = getchar()) && n < MaxPLength)
{
if(' ' != ch)
buffer[n++] = ch;
}
buffer[n] = '\0';
/* printf("%s", buffer);*/
if(CheckP(buffer))
{
/*填写入产生式结构体*/
pRNode *pt, *qt;
P[i].lCursor = IndexCh(buffer[0]);
pt = (pRNode*)malloc(sizeof(pRNode));
pt->rCursor = IndexCh(buffer[3]);
pt->next = NULL;
P[i].rHead = pt;
n = 4;
while('\0' != buffer[n])
{
qt = (pRNode*)malloc(sizeof(pRNode));
qt->rCursor = IndexCh(buffer[n]);
qt->next = NULL;
pt->next = qt;
pt = qt;
n++;
}
P[i].rLength = n - 3;
i++;
/*调试时使用*/
}
else
printf("输入符号含非法在成分,请重新输入!\n");
}
}
/*判断产生式正确性*/
bool CheckP(char * st)
{
int n;
if(100 > IndexCh(st[0]))
return false;
if('-' != st[1])
return false;
if('>' != st[2])
return false;
for(n = 3; '\0' != st[n]; n ++)
{
if(-1 == IndexCh(st[n]))
return false;
}
return true;
}
/*====================first & follow======================*/
/*计算first集,U->xx...*/
void First(int U)
{
int i,j;
for(i = 0; i < PNum; i++)
{
if(P[i].lCursor == U)
{
struct pRNode* pt;
pt = P[i].rHead;
j = 0;
while(j < P[i].rLength)
{
if(100 > pt->rCursor)
{
/*注:此处因编程出错,使空产生式时
rlength同样是1,故此处同样可处理空产生式*/
AddFirst(U, pt->rCursor);
break;
}
else
{
if(NULL == first[pt->rCursor - 100])
{
First(pt->rCursor);
}
AddFirst(U, pt->rCursor);
if(!HaveEmpty(pt->rCursor))
{
break;
}
else
{
pt = pt->next;
}
}
j++;
}
if(j >= P[i].rLength) /*当产生式右部都能推出空时*/
AddFirst(U, -1);
}
}
}
/*加入first集*/
void AddFirst(int U, int nCh) /*当数值小于100时nCh为Vt*/
/*当处理非终结符时,AddFirst不添加空项(-1)*/
{
struct collectNode *pt, *qt;
int ch; /*用于处理Vn*/
pt = NULL;
qt = NULL;
if(nCh < 100)
{
pt = first[U - 100];
while(NULL != pt)
{
if(pt->nVt == nCh)
break;
else
{
qt = pt;
pt = pt->next;
}
}
if(NULL == pt)
{
pt = (struct collectNode *)malloc(sizeof(struct collectNode));
pt->nVt = nCh;
pt->next = NULL;
if(NULL == first[U - 100])
{
first[U - 100] = pt;
}
else
{
qt->next = pt; /*qt指向first集的最后一个元素*/
}
pt = pt->next;
}
}
else
{
pt = first[nCh - 100];
while(NULL != pt)
{
ch = pt->nVt;
if(-1 != ch)
{
AddFirst(U, ch);
}
pt = pt->next;
}
}
}
/*判断first集中是否有空(-1)*/
bool HaveEmpty(int nVn)
{
if(nVn < 100) /*为终结符时(含-1),在follow集中用到*/
return false;
struct collectNode *pt;
pt = first[nVn - 100];
while(NULL != pt)
{
if(-1 == pt->nVt)
return true;
pt = pt->next;
}
return false;
}
/*计算follow集,例:U->xVy,U->xV.(注:初始符必含#——"-1")*/
void Follow(int V)
{
int i;
struct pRNode *pt ;
if(100 == V) /*当为初始符时*/
AddFollow(V, -1, 0 );
for(i = 0; i < PNum; i++)
{
pt = P[i].rHead;
while(NULL != pt && pt->rCursor != V) /*注此不能处理:U->xVyVz的情况*/
pt = pt->next;
if(NULL != pt)
{
pt = pt->next; /*V右侧的符号*/
if(NULL == pt) /*当V后为空时V->xV,将左符的follow集并入V的follow集中*/
{
if(NULL == follow[P[i].lCursor - 100] && P[i].lCursor != V)
{
Follow(P[i].lCursor);
}
AddFollow(V, P[i].lCursor, 0);
}
else /*不为空时V->xVy,(注意:y->),调用AddFollow加入Vt或y的first集*/
{
while(NULL != pt && HaveEmpty(pt->rCursor))
{
AddFollow(V, pt->rCursor, 1); /*y的前缀中有空时,加如first集*/
pt = pt->next;
}
if(NULL == pt) /*当后面的字符可以推出空时*/
{
if(NULL == follow[P[i].lCursor - 100] && P[i].lCursor != V)
{
Follow(P[i].lCursor);
}
AddFollow(V, P[i].lCursor, 0);
}
else /*发现不为空的字符时*/
{
AddFollow(V, pt->rCursor, 1);
}
}
}
}
}
/*当数值小于100时nCh为Vt*/
/*#用-1表示,kind用于区分是并入符号的first集,还是follow集
kind = 0表加入follow集,kind = 1加入first集*/
void AddFollow(int V, int nCh, int kind)
{
struct collectNode *pt, *qt;
int ch; /*用于处理Vn*/
pt = NULL;
qt = NULL;
if(nCh < 100) /*为终结符时*/
{
pt = follow[V - 100];
while(NULL != pt)
{
if(pt->nVt == nCh)
break;
else
{
qt = pt;
pt = pt->next;
}
}
if(NULL == pt)
{
pt = (struct collectNode *)malloc(sizeof(struct collectNode));
pt->nVt = nCh;
pt->next = NULL;
if(NULL == follow[V - 100])
{
follow[V - 100] = pt;
}
else
{
qt->next = pt; /*qt指向follow集的最后一个元素*/
}
pt = pt->next;
}
}
else /*为非终结符时,要区分是加first还是follow*/
{
if(0 == kind)
{
pt = follow[nCh - 100];
while(NULL != pt)
{
ch = pt->nVt;
AddFollow(V, ch, 0);
pt = pt->next;
}
}
else
{
pt = first[nCh - 100];
while(NULL != pt)
{
ch = pt->nVt;
if(-1 != ch)
{
AddFollow(V, ch, 1);
}
pt = pt->next;
}
}
}
}
/*输出first或follow集*/
void ShowCollect(struct collectNode **collect)
{
int i;
struct collectNode *pt;
i = 0;
while(NULL != collect[i])
{
pt = collect[i];
printf("\n%c:\t", Vn[i]);
while(NULL != pt)
{
if(-1 != pt->nVt)
{
printf(" %c", Vt[pt->nVt]);
}
else
printf(" #");
pt = pt->next;
}
i++;
}
printf("\n");
}
/*计算first和follow*/
void FirstFollow()
{
int i;
i = 0;
while('\0' != Vn[i])
{
if(NULL == first[i])
First(100 + i);
i++;
}
i = 0;
while('\0' != Vn[i])
{
if(NULL == follow[i])
Follow(100 + i);
i++;
}
}
/*=================构造预测分析表,例:U::xyz=============*/
void CreateAT()
{
int i;
struct pRNode *pt;
struct collectNode *ct;
for(i = 0; i < PNum; i++)
{
pt = P[i].rHead;
while(NULL != pt && HaveEmpty(pt->rCursor))
{
/*处理非终结符,当为终结符时,定含空为假跳出*/
ct = first[pt->rCursor - 100];
while(NULL != ct)
{
if(-1 != ct->nVt)
analyseTable[P[i].lCursor - 100][ct->nVt] = i;
ct = ct->next;
}
pt = pt->next;
}
if(NULL == pt)
{
/*NULL == pt,说明xyz->,用到follow中的符号*/
ct = follow[P[i].lCursor - 100];
while(NULL != ct)
{
if(-1 != ct->nVt)
analyseTable[P[i].lCursor - 100][ct->nVt] = i;
else /*当含有#号时*/
analyseTable[P[i].lCursor - 100][vtNum] = i;
ct = ct->next;
}
}
else
{
if(100 <= pt->rCursor) /*不含空的非终结符*/
{
ct = first[pt->rCursor - 100];
while(NULL != ct)
{
analyseTable[P[i].lCursor - 100][ct->nVt] = i;
ct = ct->next;
}
}
else /*终结符或者空*/
{
if(-1 == pt->rCursor) /*-1为空产生式时*/
{
ct = follow[P[i].lCursor - 100];
while(NULL != ct)
{
if(-1 != ct->nVt)
analyseTable[P[i].lCursor - 100][ct->nVt] = i;
else /*当含有#号时*/
analyseTable[P[i].lCursor - 100][vtNum] = i;
ct = ct->next;
}
}
else /*为终结符*/
{
analyseTable[P[i].lCursor - 100][pt->rCursor] = i;
}
}
}
}
}
/*输出分析表*/
void ShowAT()
{
int i,j;
printf("构造预测分析表如下:\n");
printf("\t|\t");
for(i = 0; i < vtNum; i++)
{
printf("%c\t", Vt[i]);
}
printf("#\t\n");
printf("- - -\t|- - -\t");
for(i = 0; i <= vtNum; i++)
printf("- - -\t");
printf("\n");
for(i = 0; i < vnNum; i++)
{
printf("%c\t|\t", Vn[i]);
for(j = 0; j <= vtNum; j++)
{
if(-1 != analyseTable[i][j])
printf("R(%d)\t", analyseTable[i][j]);
else
printf("error\t");
}
printf("\n");
}
}
/*=================主控程序=====================*/
void Identify(char *st)
{
int current,step,r; /*r表使用的产生式的序号*/
printf("\n%s的分析过程:\n", st);
printf("步骤\t分析符号栈\t当前指示字符\t使用产生式序号\n");
step = 0;
current = 0; /*符号串指示器*/
printf("%d\t",step);
ShowStack();
printf("\t\t%c\t\t- -\n", st[current]);
while('#' != st[current])
{
if(100 > analyseStack[topAnalyse]) /*当为终结符时*/
{
if(analyseStack[topAnalyse] == IndexCh(st[current]))
{
/*匹配出栈,指示器后移*/
Pop();
current++;
step++;
printf("%d\t", step);
ShowStack();
printf("\t\t%c\t\t出栈、后移\n", st[current]);
}
else
{
printf("%c-%c不匹配!", analyseStack[topAnalyse], st[current]);
printf("此串不是此文法的句子!\n");
return;
}
}
else /*当为非终结符时*/
{
r = analyseTable[analyseStack[topAnalyse] - 100][IndexCh(st[current])];
if(-1 != r)
{
Push(r); /*产生式右部代替左部,指示器不移动*/
step++;
printf("%d\t", step);
ShowStack();
printf("\t\t%c\t\t%d\n", st[current], r);
}
else
{
printf("无可用产生式,此串不是此文法的句子!\n");
return;
}
}
}
if('#' == st[current])
{
if(0 == topAnalyse && '#' == st[current])
{
step++;
printf("%d\t", step);
ShowStack();
printf("\t\t%c\t\t分析成功!\n", st[current]);
printf("%s是给定文法的句子!\n", st);
}
else
{ while(topAnalyse > 0)
{ if(100 > analyseStack[topAnalyse]) /*当为终结符时*/
{ printf("无可用产生式,此串不是此文法的句子!\n");
return;
}
else
{ r = analyseTable[analyseStack[topAnalyse] - 100][vtNum];
if(-1 != r)
{ Push(r); /*产生式右部代替左部,指示器不移动*/
step++;
printf("%d\t", step);
ShowStack();
if(0 == topAnalyse && '#' == st[current])
{ printf("\t\t%c\t\t分析成功!\n", st[current]);
printf("%s是给定文法的句子!\n", st);
}
else
printf("\t\t%c\t\t%d\n", st[current], r); }
else
{ printf("无可用产生式,此串不是此文法的句子!\n");
return; }
}
}
}
}
}
/*初始化栈及符号串*/
void InitStack()
{ int i;
/*分析栈的初始化*/
for(i = 0; i < MaxStLength; i++)
st[i] = '\0';
analyseStack[0] = -1; /*#(-1)入栈*/
analyseStack[1] = 100; /*初始符入栈*/
topAnalyse = 1;
}
/*显示符号栈中内容*/
void ShowStack()
{ int i;
for(i = 0; i <= topAnalyse; i++)
{ if(100 <= analyseStack[i])
printf("%c", Vn[analyseStack[i] - 100]);
else
{ if(-1 != analyseStack[i])
printf("%c", Vt[analyseStack[i]]);
else
printf("#");
}
}
}
/*栈顶出栈*/
void Pop()
{ topAnalyse--;
}
/*使用产生式入栈操作*/
void Push(int r)
{ int i;
struct pRNode *pt;
Pop();
pt = P[r].rHead;
if(-1 == pt->rCursor) /*为空产生式时*/
return;
topAnalyse += P[r].rLength;
for(i = 0; i < P[r].rLength; i++)
{ /*不为空产生式时*/
analyseStack[topAnalyse - i] = pt->rCursor;/*逆序入栈*/
pt = pt->next;
}/*循环未完时pt为空,则说明rLength记录等出错*/
}