LL(1)语法分析实现
一、 实验目的
设计一个LL(1)语法分析器，利用语法分析器对符号串的识别，加深对语法分析原理的理解。
二、 实验内容
设计并实现一个LL(1)语法分析器，实现对算术文法G[E]:E->E+T|T T->TF|F F->(E)|i所定义的符号串进行识别，例如符号串(string1.txt) abc+age+80为文法所定义的句子，符号串(string2.txt) (abc-80(s5)不是文法所定义的句子。
三、 实验要求
-
检测左递归，如果有则进行消除，实现remove_left_recursion()函数；消除直接左递归（已实现）。
-
求解FIRST集和FOLLOW集，分别实现getFirst()和getFollow()函数；
-
理解构建LL(1)分析表getTable()中的代码，实现格式打印分析表的功能（显示Table部分）；
-
对于输入符号串，实现自顶向下的LL(1)分析，打印出分析过程：AnalyzePredict函数。
四、 运行结果
测试源文件：
E->T|E+T;
T->F|T*F;
F->i|(E);
1.解析文法
| 原文法 | 消除左递归后 | |
|---|---|---|
| 规格显示 |  |
 |
| FIRST集 |  |
 |
| FOLLOW集 |  |
 |
| Table表 |  |
 |
2.语法分析
1)对string1 (string1.txt)的tocken(out1.txt)进行语法分析
| String1.txt | out1.txt |
|---|---|
 |
 |
分析结果parse_result1.txt
2)对string2 (string2.txt)的tocken(out2.txt)进行语法分析
| String2.txt | Out2.txt |
|---|---|
 |
 |
分析结果parse_result2.txt
实验代码:
parse_my.cpp
#include <iostream>
#include <string>
#include <fstream>
#include <set>
#include <map>
#include <iomanip>
#include <stack>
#include <string.h>
#include "stdlib.h"
#include <filesystem>
// namespace fs = std::filesystem;
using namespace std;
const int maxnlen = 1e4;
class Grammar
{
// @ 代表 ε 空
private:
set<char> Vn; // 非终结符
set<char> Vt; // 终结符
char S;
map<char, set<string>> P;
map<char, set<char>> FIRST;
map<char, set<char>> FOLLOW;
map<string, string> Table;
public:
Grammar(string filename)
{
Vn.clear();
Vt.clear();
P.clear();
FIRST.clear();
FOLLOW.clear();
ifstream in(filename);
if (!in.is_open())
{
cout << "文法 文件打开失败" << endl;
exit(1);
}
char *buffer = new char[maxnlen];
in.getline(buffer, maxnlen, '#'); // ??不需要txt里加上#吗??
string temps = "";
bool is_sethead = 0;
for (int i = 0; i < strlen(buffer); i++)
{
if (buffer[i] == '\n' || buffer[i] == ' ')
continue;
if (buffer[i] == ';')
{
if (!is_sethead)
{
this->setHead(temps[0]);
is_sethead = 1;
}
this->add(temps);
temps = "";
}
else
temps += buffer[i];
}
delete buffer;
// 输出Vn，Vt，set
cout << "Vn: ";
for (auto item : Vn)
{
cout << item << ", ";
}
cout << endl;
cout << "Vt: ";
for (auto item : Vt)
{
cout << item << ", ";
}
cout << endl;
}
void setHead(char c)
{
S = c;
}
// 加入产生式
void add(string s)
{
char s1 = s[0];
string s2 = "";
int num = 0;
for (int i = 0; i < s.length(); i++)
{
// 添加产生式右部
if (s[i] == '>')
num = i;
if (num == 0)
continue;
if (i > num)
s2 += s[i];
}
s2 += ';';
Vn.insert(s1);
string temp = "";
//set<char>::iterator iter1 = s2.begin();
for (int i = 0; i < s2.length(); i++)
{ //char s : s2
char s = s2[i];
if (!isupper(s) && s != '|' && s != ';' && s != '@')
Vt.insert(s);
if (s == '|' || s == ';')
{
P[s1].insert(temp);
temp = "";
}
else
{
temp += s;
}
}
}
void print()
{
cout << "当前分析文法为：" << endl
<< endl;
for (set<char>::iterator it = Vn.begin(); it != Vn.end(); it++)
{
char cur_s = *it;
for (set<string>::iterator it1 = P[cur_s].begin(); it1 != P[cur_s].end(); it1++)
{
string cur_string = *it1;
cout << cur_s << "->" << cur_string << endl;
}
}
}
void getFirst()
{
FIRST.clear();
//判断迭代次数
int iter = 4;
while (iter--)
{
for (set<char>::iterator it = Vn.begin(); it != Vn.end(); it++)
{
char left = *it;
/*请编程实现以下功能
***************************************************************************************
cur_s->cur_string[0]
a加到A的FIRST集
cur_s->cur_string[0]
B的FITRST集加到A的FIRST集
*/
bool have_null = true;
for (set<string>::iterator it1 = P[left].begin(); it1 != P[left].end(); it1++)
{
string right = *it1;
for (char V : right)
{
if (isVt(V))
{ // 是终结符则直接添加(set自动去重)
FIRST[left].insert(V);
if (V != '@')
{
break;
}
}
else
{
union_set(FIRST[left], FIRST[V]);
if (FIRST[V].count('@') > 0)
{ // 有空则加入 (set自动去重)
FIRST[left].insert('@');
}
else
{ // 没有空则退出, 不判断下一个符号
break;
}
}
}
}
}
}
//输出FIRST集
cout << "FIRST集为：" << endl
<< endl;
for (set<char>::iterator it = Vn.begin(); it != Vn.end(); it++)
{
char V = *it;
cout << "FIRST(" << V << ") : ";
for (set<char>::iterator it1 = FIRST[V].begin(); it1 != FIRST[V].end(); it1++)
{
cout << *it1 << " ";
}
cout << endl;
}
}
void getFollow()
{
FOLLOW.clear();
FOLLOW[S].insert('$');
//判断迭代次数
int iter = 4;
while (iter--)
{
for (set<char>::iterator it = Vn.begin(); it != Vn.end(); it++)
{
char left = *it;
/*请编程实现以下功能
***************************************************************************************
cur_s->cur_string[0]
a加到A的FIRST集
cur_s->cur_string[0]
B的FITRST集加到A的FIRST集
*/
for (set<string>::iterator it1 = P[left].begin(); it1 != P[left].end(); it1++)
{
string right_string = *it1;
for (int i = 1; i < right_string.length(); i++)
{
/*第一步：
B->Ac
将c加到A的follow集
*/
if (isVt(right_string[i]) && isVn(right_string[i - 1]))
{
FOLLOW[right_string[i - 1]].insert(right_string[i]);
}
/*第二步：
B->AC
将C的first集加到A的follow集
*/
if (isVn(right_string[i]) && isVn(right_string[i - 1]))
{
set<char> temp_first;
for (char V : FIRST[right_string[i]])
{
if (V != '@')
{
temp_first.insert(V);
}
}
union_set(FOLLOW[right_string[i - 1]], temp_first);
}
}
/* 第三步：
AC/ACK为最后两个或者三个
B->AC
B->ACK(K的first集含有@)
将B的follow集加入到C的follow集
*/
union_set(FOLLOW[right_string[right_string.length() - 1]],
FOLLOW[left]);
if (FIRST[right_string[right_string.length() - 1]].count('@') > 0)
{
if (isVn(right_string[right_string.length() - 2]))
{
union_set(FOLLOW[right_string[right_string.length() - 2]],
FOLLOW[left]);
}
}
}
}
}
//输出FOLLOW集
cout << "FOLLOW集为：" << endl
<< endl;
for (set<char>::iterator it = Vn.begin(); it != Vn.end(); it++)
{
char cur_s = *it;
cout << "FOLLOW(" << cur_s << ") : ";
for (set<char>::iterator it1 = FOLLOW[cur_s].begin(); it1 != FOLLOW[cur_s].end(); it1++)
{
cout << *it1 << " ";
}
cout << endl;
}
}
void getTable()
{
set<char> Vt_temp;
//int i = 0; i < s2.length() ; i++
//set<char>::iterator iter1;
for (set<char>::iterator iter1 = Vt.begin(); iter1 != Vt.end(); iter1++)
{
//char c=Vt[iter1];
Vt_temp.insert(*iter1);
}
Vt_temp.insert('$');
for (auto it = Vn.begin(); it != Vn.end(); it++)
{
char cur_s = *it;
for (auto it1 = P[cur_s].begin(); it1 != P[cur_s].end(); it1++)
{
/*
产生式为
cur_s->cur_string
*/
string cur_string = *it1;
if (isupper(cur_string[0]))
{
char first_s = cur_string[0];
for (auto it2 = FIRST[first_s].begin(); it2 != FIRST[first_s].end(); it2++)
{
string TableLeft = "";
TableLeft = TableLeft + cur_s + *it2;
Table[TableLeft] = cur_string;
}
}
else
{
string TableLeft = "";
TableLeft = TableLeft + cur_s + cur_string[0];
Table[TableLeft] = cur_string;
}
}
if (FIRST[cur_s].count('@') > 0)
{
for (auto it1 = FOLLOW[cur_s].begin(); it1 != FOLLOW[cur_s].end(); it1++)
{
string TableLeft = "";
TableLeft = TableLeft + cur_s + *it1;
Table[TableLeft] = "@";
}
}
}
/*
检查出错信息：即表格中没有出现过的
*/
for (auto it = Vn.begin(); it != Vn.end(); it++)
{
for (auto it1 = Vt_temp.begin(); it1 != Vt_temp.end(); it1++)
{
string TableLeft = "";
TableLeft = TableLeft + *it + *it1;
if (!Table.count(TableLeft))
{
Table[TableLeft] = "error";
}
}
}
/*请编程实现以下功能
***************************************************************************************
显示Table，例如格式打印：cout << *it << "->" << setw(7) << Table[iter];
*/
cout << "显示table表：" << endl
<< endl;
for (auto iter = Table.begin(); iter != Table.end(); iter++)
{
char Vn_item = iter->first[0];
char Vt_item = iter->first[1];
string exp = iter->second;
cout << "[" << Vn_item << "]"
<< " meet "
<< "[" << Vt_item << "] "
<< "chose: " << Vn_item << " -> " << exp << endl;
}
}
/*
每一次分析一个输入串
Sign为符号栈,出栈字符为x
输入字符串当前字符为a
*/
bool AnalyzePredict(string inputstring)
{
string Sign; // 字符串表示符号栈
Sign += '$';
Sign += S;
int StringPtr = 0;
cout << setw(20) << right << "栈 "
<< setw(20) << left << " 剩余输入"
<< setw(20) << left << " 输出" << endl;
// char a = inputstring[StringPtr++];
char a = inputstring[StringPtr];
bool flag = true;
while (flag)
{
cout << endl
<< setw(20) << right << Sign + " "
<< setw(20) << left << inputstring.substr(StringPtr, inputstring.length() - StringPtr);
char x = Sign[Sign.length() - 1];
Sign = Sign.substr(0, Sign.length() - 1);
//如果是终结符,直接移出符号栈
if (Vt.count(x))
{
if (x == a)
{
cout << "出栈:" << a;
a = inputstring[++StringPtr];
}
else if (x == '@')
{
cout << "出栈:@";
continue;
}
else
{
cout << "终结符不匹配 " << x << " index: " << StringPtr << endl;
return false;
}
}
else
{
/*请编程实现以下功能
***************************************************************************************
*/
if (x == '$')
{ //第一步：如果不是终结符，如果是末尾符号
if (a == '$')
{
cout << "分析结束";
return true;
}
else
{
cout << "字符串未推导完毕 ";
while (StringPtr < inputstring.length())
{
cout << inputstring[StringPtr++];
}
cout << " index: " << StringPtr << endl;
return false;
}
}
else
{ //第二步：如果是非终结符，需要移进操作
string reduc_str = " ";
reduc_str[0] = x;
reduc_str += a;
// cout << reduc_str << endl;
if (Table[reduc_str] == "error")
{
cout << "移进错误: " << reduc_str << " index: " << StringPtr << endl;
return false;
}
for (int i = Table[reduc_str].length() - 1; i >= 0; i--)
{
Sign += Table[reduc_str][i];
}
cout << "[" << reduc_str[0] << "]"
<< " meet "
<< "[" << reduc_str[1] << "] "
<< "chose: " << reduc_str[0] << " -> " << Table[reduc_str];
// a = inputstring[StringPtr++];
}
}
}
return true;
}
/*
消除左递归算法蓝书P124
*/
void remove_left_recursion()
{
string tempVn = "";
for (auto it = Vn.begin(); it != Vn.end(); it++)
{
tempVn += *it;
}
for (int i = 0; i < tempVn.length(); i++)
{
char pi = tempVn[i];
/*请编程实现消除左递归的替换代入操作
***************************************************************************************
*/
for (int j = 0; j < i; j++)
{
char pj = tempVn[j];
set<string> temp_pi_set;
for (string right_single : P[pi])
{
temp_pi_set.insert(right_single);
}
for (string right_single : P[pi])
{
bool find_pj = false; // 找到后, 替换完后, 删除right_single
if (right_single.find(pj) != right_single.npos)
{
// cout << "place: " << right_single.find(pj) << endl;
find_pj = true;
for (string to_replace : P[pj])
{
// cout << "pos:" << right_single.find(pj) << " size:" << right_single.size() << endl;
string right_single_temp = right_single;
string replaced = right_single_temp.replace(right_single_temp.find(pj), 1, to_replace);
temp_pi_set.insert(replaced);
}
}
if (find_pj)
{
temp_pi_set.erase(right_single);
}
}
P[pi] = temp_pi_set;
}
remove_left_gene(pi);
}
}
/*
消除直接左递归
*/
void remove_left_gene(char c)
{
char NewVn;
for (int i = 0; i < 26; i++)
{
NewVn = i + 'A';
if (!Vn.count(NewVn))
{
break;
}
}
bool isaddNewVn = 0;
for (auto it = P[c].begin(); it != P[c].end(); it++)
{
string right = *it;
if (right[0] == c)
{
isaddNewVn = 1;
break;
}
}
if (isaddNewVn)
{
set<string> NewPRight; //加入了新非终结符NewVn的右部
set<string> NewPNewVn; //新非终结符的右部
for (auto it = P[c].begin(); it != P[c].end(); it++)
{
string right = *it;
if (right[0] != c)
{
right += NewVn; //TA
NewPRight.insert(right);
}
else
{
right = right.substr(1); //+TA
right += NewVn;
NewPNewVn.insert(right);
}
}
Vn.insert(NewVn);
NewPNewVn.insert("@");
Vt.insert('@');
P[NewVn] = NewPNewVn;
P[c] = NewPRight;
}
}
void ShowByTogether()
{
for (auto it = Vn.begin(); it != Vn.end(); it++)
{
cout << *it << "->";
char c = *it;
for (auto it1 = P[c].begin(); it1 != P[c].end(); it1++)
{
if (it1 == P[c].begin())
cout << *it1;
else
cout << "|" << *it1;
}
cout << endl;
}
}
bool isVn(char V)
{
if (Vn.find(V) != Vn.end())
{
return true;
}
else
{
return false;
}
}
bool isVt(char V)
{
if (Vt.find(V) != Vt.end())
{
return true;
}
else
{
return false;
}
}
template <typename T>
static void union_set(set<T> &set1, set<T> &set2)
{
for (T item : set2)
{
set1.insert(item);
}
}
};
int main()
{
/*
文法测试
E->T|E+T;
T->F|T*F;
F->i|(E);
A->+TA|@;
B->*FB|@;
E->TA;
F->(E)|i;
T->FB;
直接将上面两个测试样例放在parse_test1.txt和parse_test2.txt中
*/
string pwd = "C:\\Users\\46855\\Desktop\\c\\grammaticalAnalysis\\";
string filename_gramer = pwd + "parse_test1.txt";
//将标准输出重定向到 parse_result.txt文件
// freopen((pwd + "parse_result1.txt").c_str(), "w", stdout);
freopen((pwd + "parse_result2.txt").c_str(), "w", stdout);
Grammar *grammar = new Grammar(filename_gramer);
cout << "/-------------------------没有消除左递归-----------------------------/" << endl;
cout << "规格显示：" << endl;
grammar->ShowByTogether();
cout << endl;
grammar->getFirst();
cout << endl;
grammar->getFollow();
cout << endl;
grammar->getTable();
cout << "/--------------------------------------------------------------------/" << endl
<< endl
<< endl;
cout << "/-------------------------已经消除左递归-----------------------------/" << endl;
/*
消除左递归之后的判断
*/
grammar->remove_left_recursion();
cout << "规格显示：" << endl;
cout << endl;
grammar->ShowByTogether();
grammar->getFirst();
cout << endl;
grammar->getFollow();
cout << endl;
grammar->getTable();
cout << "/--------------------------------------------------------------------/" << endl
<< endl
<< endl;
cout << "/-------------------------对词法进行分析----------------------------/" << endl;
/*
目前的想法是使用第一个实验lex.cpp文件分离出不同的单词，然后对单词进行操作：
如果单词为+，*，等于他本身，否则等于i;
以下直接使用lex.cpp运行后的输出文本out1.txt（见Parsing文件夹内）
*/
// string filename = pwd + "\\Parsing\\out1.txt";
string filename = pwd + "\\Parsing\\out2.txt";
ifstream in(filename);
char buffer[200];
string inf = "";
int num = 0;
// cout << "文法分析结果为：" << endl << endl;
if (in.is_open())
{
while (!in.eof())
{
in.getline(buffer, 100);
// cout << buffer << endl;
inf += buffer;
num++;
}
}
string row = "";
for (int i = 0; i < num - 1; i++)
{
int ptr = i * 13;
string temp = "";
for (int j = 1; j <= 5; j++)
{
if (inf[j + ptr] == ' ')
continue;
else
temp += inf[ptr + j];
}
if (temp == "+" || temp == "-" || temp == "*" || temp == "/" || temp == ">" || temp == "<" || temp == "=" || temp == "(" || temp == ")")
{
row += temp;
}
else
{
if (temp == ";")
{
row += "$";
cout << "当前输入串row为: " << row << endl
<< endl;
if (grammar->AnalyzePredict(row))
{
cout << endl
<< " √正确" << endl;
}
else
cout << endl
<< " ×错误" << endl;
row = "";
}
else
{
row += "i";
}
}
}
cout << "/--------------------------------------------------------------------/" << endl
<< endl
<< endl;
system("pause");
return 0;
}
lex.cpp
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <iomanip>
#include <string.h>
using namespace std;
const int maxn = 1e4;
const int maxlen = 1e4;
char operate[11][10] = { "+","-","*","/",">","<","=","(",")",";" ,"|"};
char keyword[5][10] = { "if","then","else","while","do" };
class lexical {
private:
static const int rowope = 11;//操作符个数
static const int rowkey = 5;//关键字个数
struct Twotuples {
char kind[10];
char proper[10];
}tuples[maxlen];
string filename;
public:
bool isCal(char *s, int &length) {
char sub[100];
for (int i = 0; i < rowope; i++) {
int len = strlen(operate[i]);
strncpy(sub, s, len);
sub[len] = '\0';
if (strcmp(sub, operate[i]) == 0) {
length = len;
return true;
}
}
return false;
}
bool isKey(char *s, int &length) {
char sub[100];
int num = 0;
while (isalpha(*(s + num))) {
num++;
}
length = num;
for (int i = 0; i < rowkey; i++) {
strncpy(sub, s, length);
sub[length] = '\0';
if (strcmp(sub, keyword[i]) == 0 && !isalpha(*(s + length))) {
return true;
}
}
return false;
}
bool isTen(char *s, int &length) {
if (s[0] == '0'&&!isdigit(s[1]) && s[1] != 'x') {
length = 1;
return true;
}
else
if (s[0] >= '1'&&s[0] <= '9') {
int num = 0;
while (isdigit(*(s + num))) {
num++;
}
length = num;
return true;
}
return false;
}
bool isEight(char *s, int &length) {
if (s[0] == '0' && (s[1] >= '1'&&s[1] <= '7')) {
int num = 0;
while (s[num] >= '0'&&s[num] <= '7') {
num++;
cout<<"1";
}
length = num;
return true;
}
return false;
}
bool isSixteen(char *s, int &length) {
if (s[0] == '0' && s[1] == 'x' && ((s[2] >= '0'&&s[2] <= '9') || (s[2] >= 'a'&&s[2] <= 'f'))) {
int num = 2;
while ((s[num] >= '0'&&s[num] <= '9') || (s[num] >= 'a'&&s[num] <= 'f')) {
num++;
cout<<"2";
}
length = num;
return true;
}
return false;
}
void scan(char *str, int &p1, int &p2) {
int len = 0;
char str_[] = "-";
char sub[100];
//运算符和界符
if (isCal(str + p1, len)) {
strncpy(sub, str + p1, len);
sub[len] = '\0';
strcpy(tuples[p2].kind, sub);
strcpy(tuples[p2].proper, str_);
p1 += len;
p2++;
}
//关键字
if (isKey(str + p1, len)) {
strncpy(sub, str + p1, len);
sub[len] = '\0';
strcpy(tuples[p2].kind, sub);
strcpy(tuples[p2].proper, str_);
p1 += len;
p2++;
}
//标识符
if (isalpha(*(str + p1))) {
int len = 0;
while (isalpha(*(str + p1 + len)) || isdigit(*(str + p1 + len))) {
len++;
cout<<"3";
}
strncpy(sub, str + p1, len);
sub[len] = '\0';
strcpy(tuples[p2].kind, "0");
strcpy(tuples[p2].proper, sub);
p1 += len;
p2++;
}
//十进制数字
if (isTen(str + p1, len)) {
strncpy(sub, str + p1, len);
sub[len] = '\0';
strcpy(tuples[p2].kind, "1");
strcpy(tuples[p2].proper, sub);
p1 += len;
p2++;
}
if (isEight(str + p1, len)) {
strncpy(sub, str + p1 + 1, len - 1);
sub[len - 1] = '\0';
strcpy(tuples[p2].kind, "2");
strcpy(tuples[p2].proper, sub);
p1 += len;
p2++;
}
if (isSixteen(str + p1, len)) {
strncpy(sub, str + p1 + 2, len - 2);
sub[len - 2] = '\0';
strcpy(tuples[p2].kind, "3");
strcpy(tuples[p2].proper, sub);
p1 += len;
p2++;
}
}
lexical(string inputfile , string outputfile) {
this->filename = inputfile;
char *buffer = new char[maxlen];
ifstream in(filename);
if (!in.is_open()) {
cout << "文件打开失败" << endl;
exit(1);
}
in.getline(buffer, maxlen, '#');
int len = strlen(buffer);
bool flagend = false;
for (int i = 0; i < strlen(buffer); i++) {
if (buffer[i] == '#') {
flagend = true;
break;
}
}
if (!flagend)buffer[len++] = '#';
buffer[len] = '\0';
cout << buffer << endl;
int buf_ptr = 0;
int tup_ptr = 0;
while (true) {
if (buffer[buf_ptr] == '#')break;
if (buffer[buf_ptr] == ' ' || buffer[buf_ptr] == '\n') {
buf_ptr++;
continue;
}
if (buffer[buf_ptr] == '\t') {
buf_ptr += 4;
continue;
}
scan(buffer, buf_ptr, tup_ptr);
}
cout.setf(std::ios::left);
ofstream out(outputfile);
for (int i = 0; i < tup_ptr; i++) {
out << "<" << setw(5) << tuples[i].kind << "," << setw(5) << tuples[i].proper << ">" << endl;
cout << "<" << setw(5) << tuples[i].kind << "," << setw(5) << tuples[i].proper << ">" << endl;
}
}
};
int main()
{
string pwd = "C:\\Users\\46855\\Desktop\\c\\grammaticalAnalysis\\";
// string filename1 = pwd + "parse_test1.txt";
// string filename1 = pwd + "string1.txt";
// string filename2= pwd + "Parsing\\out1.txt";
string filename1 = pwd + "string2.txt";
string filename2= pwd + "Parsing\\out2.txt";
lexical *text = new lexical(filename1,filename2);
system("pause");
return 0;
}
