使用C++ 完成LR(0)的语法分析器
由于最近学校里在学习编译原理，而且要求实现语法分析器，于是我用了几天的时间搞明白了语法分析器的原理并且将其实现了。由于编者还是本科生而且还在学习中，因此出现什么错误请各位指点。
语法分析器的步骤为：
- 读入单词序列
- 读入语法规则
- 构造基于该语法的Clousure（项目集规范族）集合
- 基于上一步构造所有规范句型活前缀的DFA
- 根据这个DFA来构造Action表与Goto表（统称为分析表）
- 根据分析表来进行分析（具体的分析方法不再赘述）
由于编者对于所有的处理都是使用字符串与字符进行的，所以在代码理解方面与执行效率方面可能较差。有什么问题都可以与笔者交流，我的Q是1574143668。
所以相应的代码如下，使用的是IDE是Visual Studio 2017，可以供大家参考：
具体的代码文件在https://download.csdn.net/download/kiva12138/10750255
#include "pch.h"
#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <map>
#include <typeinfo>
#define MAXNUM 1000
#define ERROR "err"
#define ACCUTATE "acc"
#define MAXNUMOFCLOUSURE 100
#define MAXNUMOFITEM 100
#define MAXNUMOFCHAR 30
using namespace std;
class StatusStack{
protected:
int list[MAXNUM];
int currentPos;
public :
StatusStack() {
currentPos = -1;
}
int getTop() {
return this->list[currentPos];
}
int getCurrentPos() {
return this->currentPos;
}
int getElement(int pos) {
return this->list[pos];
}
void clear() {
currentPos = -1;
}
void pop() {
currentPos = currentPos - 1;
}
void push(int status) {
list[currentPos+1] = status;
currentPos++;
}
};
class SymbolStack {
protected:
char list[MAXNUM];
int currentPos;
public:
SymbolStack() {
list[0] = '#';
currentPos = 0;
}
char getTop() {
return this->list[currentPos];
}
int getCurrentPos() {
return this->currentPos;
}
char getElement(int pos) {
return this->list[pos];
}
void clear() {
list[0] = '#';
currentPos = 0;
}
void pop() {
currentPos = currentPos - 1;
}
void push(char str) {
list[currentPos + 1] = str;
currentPos++;
}
};
class ActionMap {//table[status, inputChar]
protected:
map <int, map<int, string> > table;
int numOfStatus;
int numOfInputChar;
public:
ActionMap(int numOfStatus, int numOfInputChar){
this->numOfInputChar = numOfInputChar;
this->numOfStatus = numOfStatus;
for (int i = 0; i < numOfStatus; i++) {
for (int j = 0; j < numOfInputChar; j++) {
table[i][j] = ERROR;
}
}
}
void insert(int status, int inputChar, string ele) {
table[status][inputChar] = ele;
}
void remove(int status, int inputChar) {
table[status][inputChar] = ERROR;
}
string getElement(int status, int inputChar) {
return table[status][inputChar];
}
};
class GotoMap {//table[status, inputStatus]
protected:
map <int, map<int, int> > table;
int numOfStatus;
int numOfInputStatus;
public:
GotoMap(int numOfStatus, int numOfInputStatus) {
this->numOfInputStatus = numOfInputStatus;
this->numOfStatus = numOfStatus;
for (int i = 0; i < numOfStatus; i++) {
for (int j = 0; j < numOfInputStatus; j++) {
table[i][j] = -1;
}
}
}
void insert(int status, int inputChar, int ele) {
table[status][inputChar] = ele;
}
void remove(int status, int inputChar) {
table[status][inputChar] = -1;
}
int getElement(int status, int inputChar) {
return table[status][inputChar];
}
};
class DFAMap {//[a, b]=B 从状态a接受B到达状态b
protected:
map <int, map<int, char> > table;
int firstStatus;
int secondStatus;
public:
DFAMap(int numOfStatus) {
this->firstStatus = numOfStatus;
this->secondStatus = numOfStatus;
for (int i = 0; i < numOfStatus; i++) {
for (int j = 0; j < numOfStatus; j++) {
table[i][j] = '*';
}
}
}
void insert(int status1, int status2, char ele) {
table[status1][status2] = ele;
}
void remove(int status1, int status2) {
table[status1][status2] = '*';
}
char getElement(int status1, int status2) {
return table[status1][status2];
}
};
class NumOfInputChar {
protected:
map<int, char> table;
int sum;
public :
NumOfInputChar() {
this->sum = 0;
}
int getSum() {
return this->sum;
}
void inset(char ch) {
table [sum++] = ch;
}
int getNumber(char ch) {
for (int i = 0; i <= sum; i++) {
if (table[i] == ch) {
return i;
}
}
return -1;
}
};
class NumOfInputStatus {
protected:
map<int, char> table;
int sum;
public:
NumOfInputStatus() {
this->sum = 0;
}
void inset(int i) {
table[sum++] = i;
}
int getNumber(int in) {
for (int i = 0; i <= sum; i++) {
if (table[i] == in) {
return i;
}
}
return -1;
}
};
class Item {
public :
int posOfDot;
string item;
public :
Item() {
for (int i = 0; i < 30; i++) {
this->item += '\0';
}
}
};
class Clousure {
public:
int numOfItem;
Item grammer[MAXNUMOFITEM];
};
void printSymbolStack(SymbolStack symbolStack) {
int num = symbolStack.getCurrentPos();
cout << "符号栈的内容为:" << endl;
for (int i = 0; i <= num; i++) {
cout << symbolStack.getElement(i) << " ";
}
cout << endl;
}
void printStatusStack(StatusStack statusStack) {
int num = statusStack.getCurrentPos();
cout << "状态栈的内容为:" << endl;
for (int i = 0; i <= num; i++) {
cout << statusStack.getElement(i) << " ";
}
cout << endl;
}
void getInputSymbol(string strInput[], int * numOfSymbol) {
//ifstream fp("input.txt");
ifstream fp("input_test.txt");
string strRead[MAXNUM];
string temp;
if (fp.fail()) {
std::cout << "Can not open the source file";
exit(0);
}
int num = 0;
while (getline(fp, temp)) {
strInput[num++] = temp;
}
*numOfSymbol = num;
}
void getGrammer(string grammerInput[], int * numOfGrammer) {
ifstream fp("grammer_test.txt");
string temp;
int grammerHasRead = 0;
if (fp.fail()) {
std::cout << "Can not open the source file";
exit(0);
}
int num = 0;
while (getline(fp, temp)) {
grammerInput[num++] = temp;
}
*numOfGrammer = num;
}
bool grammerAnalysis(string strInput[], ActionMap actionMap, GotoMap gotoMap,
StatusStack statusStack, SymbolStack symbolStack,
NumOfInputStatus numOfInputStatus, NumOfInputChar numOfInputChar,
string grammerInput[]) {
statusStack.push(0);
int i = 0;
int lastAction = 0;//记录上一动作，0表示移进， 1表示归约
while (1) {
if (lastAction == 0) {
char temp[1];
strInput[i].copy(temp, 1, 0);
char inputChar = temp[0];
string actionToDo = "";
actionToDo = actionMap.getElement(statusStack.getTop(), numOfInputChar.getNumber(inputChar));
if (actionToDo == ACCUTATE) {
return true;
}
else if (actionToDo == ERROR) {
return false;
}
if (actionToDo[0] == 'S') {
//移进操作
statusStack.push(actionToDo[1] - 48);
symbolStack.push(inputChar);
i++;
lastAction = 0;
//打印信息
cout << "移进操作:" <<"移进"<< inputChar << endl;
printStatusStack(statusStack);
printSymbolStack(symbolStack);
cout << endl;
}
else if (actionToDo[0] == 'R') {
//归约操作 使用actionToDo[1]产生式
int numOfGrammer = actionToDo[1] - 48;
int startPosOfGrammer = 0;//产生式开始的位置
int endPosOfGrammer = 0;//产生式结束的的分号的位置
char temp[1];
grammerInput[numOfGrammer-1].copy(temp, 1, endPosOfGrammer);
char todoChar = temp[0];
while (todoChar != ';') {
grammerInput[numOfGrammer-1].copy(temp, 1, endPosOfGrammer);
todoChar = temp[0];
endPosOfGrammer++;
}
endPosOfGrammer--;
int numOfPop = endPosOfGrammer - startPosOfGrammer - 1;
for (; numOfPop > 0; numOfPop--) {
symbolStack.pop();
statusStack.pop();
}
grammerInput[numOfGrammer-1].copy(temp, 1, startPosOfGrammer);
char charToPush = temp[0];
symbolStack.push(charToPush);
lastAction = 1;
//打印信息
cout << "归约操作:" << "使用第" << actionToDo[1] - 48 << "个产生式" << endl;
printStatusStack(statusStack);
printSymbolStack(symbolStack);
cout << endl;
}
else {
cout << "符号表识别错误" << endl;
getchar();
exit(0);
}
continue;
}
else if (lastAction == 1) {
int statusToGo = gotoMap.getElement(statusStack.getTop(), numOfInputStatus.getNumber(symbolStack.getTop()));
if (statusToGo == -1) {
return false;
}
statusStack.push(statusToGo);
lastAction = 0;
//打印信息
cout << "状态转移:" << "转移到第" << statusToGo << "状态" << endl;
cout << endl;
continue;
}
}
}
void makeAnalysisChart(string grammerInput[], ActionMap * actionMap, GotoMap * gotoMap,
NumOfInputChar * numOfInputChar, NumOfInputStatus * numOfInputStatus, int numOfGrammer) {
//构造Clousure, s代表S', 其余为大写S
//首先构造最基本的0与1号状态
int numOfClousure = 0;
Clousure clousure[MAXNUMOFCLOUSURE];
clousure[0].numOfItem = 1;
clousure[0].grammer[0].posOfDot = 1;
clousure[0].grammer[0].item = "s.S";
clousure[1].numOfItem = 1;
clousure[1].grammer[0].item = "sS.";
clousure[1].grammer[0].posOfDot = 2;
int numOfInitClo = 2;
for (int i = 0; i < numOfGrammer; i++) {
char chs[MAXNUMOFCHAR];
int numOfCh = 0;
for (int j = 0; j<MAXNUMOFCHAR; j++) {
char temp[1];
grammerInput[i].copy(temp, 1, j);
if (temp[0] == ';') {
break;
}
chs[j] = temp[0];
numOfCh = j;
}
for (int j = 2; j <= numOfCh+1; j++) {
clousure[numOfInitClo].numOfItem = 1;
bool b = false;
for (int k = 0; k <= numOfCh+1; k++) {
if (k == j) {
b = true;
clousure[numOfInitClo].grammer[0].item[j] = '.';
continue;
}
if (b) {
clousure[numOfInitClo].grammer[0].item[k] = chs[k-1];
}
else {
clousure[numOfInitClo].grammer[0].item[k] = chs[k];
}
}
clousure[numOfInitClo].grammer[0].posOfDot = j;
numOfInitClo++;
}
}
while (numOfClousure < numOfInitClo) {
int lastNumOfItem = clousure[numOfClousure].numOfItem;
while (1) {
char toDoChar = clousure[numOfClousure].grammer[clousure[numOfClousure].numOfItem - 1].item[clousure[numOfClousure].grammer[clousure[numOfClousure].numOfItem - 1].posOfDot + 1];
if (toDoChar == '\0') {
numOfClousure++;
break;
}
for (int i = 0; i < numOfGrammer; i++) {
char temp[1];
grammerInput[i].copy(temp, 1, 0);
char firstGrammerChar = temp[0];
if (firstGrammerChar == toDoChar) {
stringstream stream;
stream << firstGrammerChar;
string itemToInsert = stream.str() + '.';
bool ifExist = false;
for (int k = 1; ; k++) {
char tempChs[1];
grammerInput[i].copy(tempChs, 1, k);
char tempCh = tempChs[0];
if (tempCh == ';') {
break;
}
itemToInsert = itemToInsert + tempCh;
}
for (int k = 0; k < clousure[numOfClousure].numOfItem; k++) {
if (itemToInsert == clousure[numOfClousure].grammer[k].item) {
ifExist = true;
break;
}
}
if (ifExist) {
continue;
}
clousure[numOfClousure].grammer[clousure[numOfClousure].numOfItem].item = itemToInsert;
clousure[numOfClousure].grammer[clousure[numOfClousure].numOfItem].posOfDot = 1;
clousure[numOfClousure].numOfItem++;
}
}
if (lastNumOfItem == clousure[numOfClousure].numOfItem) {
numOfClousure++;
break;
}
lastNumOfItem = clousure[numOfClousure].numOfItem;
}
}
cout << "计算得出的闭包:" << endl << endl;
for (int ik = 0; ik < numOfInitClo; ik++) {
cout << "Clousure" << ik << ":" << endl;
for (int j = 0; j < clousure[ik].numOfItem; j++) {
cout << clousure[ik].grammer[j].item[0] << "->";
for (int i = 1; i <= clousure[ik].grammer[j].item.length(); i++) {
cout << clousure[ik].grammer[j].item[i];
}
cout << endl;
}
}
cout << endl;
//下面构造DFA
DFAMap * dfaMap = new DFAMap(numOfInitClo);
for (int n = 0; n < numOfInitClo; n++) {
for (int m = 0; m < clousure[n].numOfItem; m++) {
string itemToCal = clousure[n].grammer[m].item;
char chToMove = clousure[n].grammer[m].item[clousure[n].grammer[m].posOfDot+1];//需要使用的符号
if (chToMove == '\0') {
continue;
}
itemToCal[clousure[n].grammer[m].posOfDot+1] = '.';
itemToCal[clousure[n].grammer[m].posOfDot] = chToMove;
for (int t = 0; t < numOfInitClo; t++) {
for (int e = 0; e < clousure[t].numOfItem; e++) {
string itemToCmp = clousure[t].grammer[e].item;
//cout << itemToCal.c_str() << "==" << itemToCmp.c_str() << "=" << endl;
if (strcmp(itemToCal.c_str() , itemToCmp.c_str()) == 0) {
//cout << "OK"<< endl;
dfaMap->insert(n, t, chToMove);
}
}
}
}
}
//下面构造分析表
for (int k = 0; k < numOfInitClo; k++) {
if (k == 1) {//第1号一定是sS.
actionMap->insert(k, numOfInputChar->getNumber('#'), ACCUTATE);
continue;
}
for (int g = 0; g < clousure[k].numOfItem; g++) {
string tempItem = clousure[k].grammer[g].item;
if (tempItem[clousure[k].grammer[g].posOfDot+1] == '\0') {
tempItem[clousure[k].grammer[g].posOfDot] = '\0';
for (int h = 0; h < numOfGrammer; h++) {
string tempGrammmer = grammerInput[h];
tempGrammmer[tempGrammmer.length() - 1] = '\0';
if (strcmp(tempGrammmer.c_str(), tempItem.c_str()) == 0) {
//k状态 全部为R(h+1)
string str = "R" + to_string(h+1);
for (int v = 0; v < numOfInputChar->getSum(); v++) {
actionMap->insert(k, v, str);
}
break;
}
}
continue;
}
char tempCh = tempItem[clousure[k].grammer[g].posOfDot + 1];
if (numOfInputChar->getNumber(tempCh) >= 0) {
for (int d = 0; d < numOfClousure; d++) {
if (dfaMap->getElement(k, d) == tempCh) {
string tempStr = "S"+ to_string(d);
actionMap->insert(k, numOfInputChar->getNumber(tempCh), tempStr);
}
}
continue;
}
if (numOfInputStatus->getNumber(tempCh) >= 0) {
for (int d = 0; d < numOfClousure; d++) {
if (dfaMap->getElement(k, d) == tempCh) {
gotoMap->insert(k, numOfInputStatus->getNumber(tempCh),d);
}
}
continue;
}
cout << endl << "识别符号出错！" << endl;
exit(0);
}
}
}
int main()
{
int symbolNum = 0;
string inputSymbol[MAXNUM];
getInputSymbol(inputSymbol, &symbolNum);
cout << "输入序列：" << endl;
for (int i = 0; i <= symbolNum; i++) {
cout << inputSymbol[i];
}
cout << endl << endl;
int grammerNum;
string grammerInput[MAXNUM];
getGrammer(grammerInput, &grammerNum);
cout << "语法序列：" << grammerNum << "个" << endl;
for (int i = 0; i < grammerNum; i++) {
cout << grammerInput[i] << endl;
}
cout << endl;
cout << "构造语法分析表......" << endl << endl;
ActionMap *action = new ActionMap(7, 3);//7个状态， 3个终结符
NumOfInputChar *numOfInputChar = new NumOfInputChar;//与上面相对应的终结符集合
numOfInputChar->inset('a');
numOfInputChar->inset('b');
numOfInputChar->inset('#');
GotoMap *gotoMap = new GotoMap(7, 2);//7个状态，2个非终结符
NumOfInputStatus *numOfInputStatus = new NumOfInputStatus;//非终结符集合
numOfInputStatus->inset('S');
numOfInputStatus->inset('B');
makeAnalysisChart(grammerInput, action, gotoMap, numOfInputChar, numOfInputStatus, grammerNum);
//Test
cout << "Action表：" << endl;
for (int i = 0; i < 7; i++) {
for (int j = 0; j < 3; j++) {
cout << action->getElement(i, j) << " ";
}
cout << endl;
}
cout << endl;
cout << "Goto表：" << endl;
for (int i = 0; i < 7; i++) {
for (int j = 0; j < 2; j++) {
cout << gotoMap->getElement(i, j) << " ";
}
cout << endl;
}
cout << endl;
cout << "语法分析表构造完毕......" << endl << endl;
cout << "开始语法分析......" << endl << endl;
StatusStack *statusStack = new StatusStack;
SymbolStack *symbolStack = new SymbolStack;
bool result = grammerAnalysis(inputSymbol, *action, *gotoMap,
*statusStack, *symbolStack,
*numOfInputStatus, *numOfInputChar,
grammerInput);
if (result) {
cout << endl << "成功完成语法分析!" << endl << endl;
}
else {
cout << endl << "语法分析失败!" << endl << endl;
}
cout << "结束语法分析......" << endl;
getchar();
return 0;
}
最后的结果大家可以看一下：
输入序列：
bab#
语法序列：3个
S->BB;
B->aB;
B->b;
构造语法分析表......
计算得出的闭包:
Clousure0:
s->.S
S->.BB
B->.aB
B->.b
Clousure1:
s->S.
Clousure2:
S->B.B
B->.aB
B->.b
Clousure3:
S->BB.
Clousure4:
B->a.B
B->.aB
B->.b
Clousure5:
B->aB.
Clousure6:
B->b.
Action表：
S4 S6 err
err err acc
S4 S6 err
R1 R1 R1
S4 S6 err
R2 R2 R2
R3 R3 R3
Goto表：
1 2
-1 -1
-1 3
-1 -1
-1 5
-1 -1
-1 -1
语法分析表构造完毕......
开始语法分析......
移进操作:移进b
状态栈的内容为:
0 6
符号栈的内容为:
# b
归约操作:使用第3个产生式
状态栈的内容为:
0
符号栈的内容为:
# B
状态转移:转移到第2状态
移进操作:移进a
状态栈的内容为:
0 2 4
符号栈的内容为:
# B a
移进操作:移进b
状态栈的内容为:
0 2 4 6
符号栈的内容为:
# B a b
归约操作:使用第3个产生式
状态栈的内容为:
0 2 4
符号栈的内容为:
# B a B
状态转移:转移到第5状态
归约操作:使用第2个产生式
状态栈的内容为:
0 2
符号栈的内容为:
# B B
状态转移:转移到第3状态
归约操作:使用第1个产生式
状态栈的内容为:
0
符号栈的内容为:
# S
状态转移:转移到第1状态
成功完成语法分析!
结束语法分析......
最后祝大家学习愉快，大家加油！
