编译原理系列实验四语义分析与中间代码⽣成最后⼀次实验！⽬录实验四语义分析与中间代码⽣成实验⽬的通过上机实习，加深对语法制导翻译原理的理解，掌握将语法分析所识别的语法范畴变换为某种中间代码的语义翻译⽅法。
掌握⽬前普遍采⽤的语义分析⽅法──语法制导翻译技术。
给出 PL/0 ⽂法规范，要求在语法分析程序中添加语义处理，对于语法正确的表达式，输出其中间代码；对于语法正确的算术表达式，输出其计算值。
题⽬【问题描述】在实验⼆或实验三的表达式语法分析程序⾥，添加语义处理部分。
对于语法正确的表达式，输出其中间代码，⽤四元式序列表⽰；对于语法正确的算术表达式，输出其计算值。
例如：当输⼊为2+35时，程序输出为17；当输⼊为a(b+c)时，程序输出为四元式：(+,b,c,t1)(,a,t1,t2)要求源程序能智能判断这两种情况，并输出相应结果。
【输⼊形式】（1） PL/0算术表达式的语义计算。
PL/0算术表达式，例如:2+35作为输⼊。
（2）PL/0表达式的中间代码表⽰。
输⼊：PL/0表达式，例如: a*(b+c)。
【输出形式】2+35作为输⼊时，输出为17a(b+c)作为输⼊时，输出为(+,b,c,t1)(*,a,t1,t2)源程序#include <iostream>#include<bits/stdc++.h>using namespace std;/**词法分析及其结果存储**/pair<string, string> lexRes[50]; // 词法分析结果，每个pair的first如"ident"，second如"a"int lexI = 0; // lexRes的指针void lexical()/*词法分析：读⼊⼀⾏字符串，处理该字符串的词法分析结果⾄lexRes*//*lexI终为lexRes的长度，即单词数*/{// 读⼊输⼊串string inputs; // 如，a*(b+c)cin >> inputs;// 初始化词典map<string,string> words;std::map<string,string>::iterator it;words["+"]="plus";words["-"]="minus";words["*"]="times";words["/"]="slash";words["="]="eql";words["("]="lparen";words[")"]="rparen";// 开始分析int insize=inputs.length();string word; // 输⼊符号，如"a"/"123"{// 空⽩符跳过while(inputs[i] == ' ' || inputs[i] == '\n')i++;// 标志符/基本字捕捉if(isalpha(inputs[i])){// 拿出⼀个标志符/基本字word = inputs[i++];while(isalpha(inputs[i]) || isdigit(inputs[i]))word += inputs[i++];// 在map中找到相应的词性，并输出it = words.find(word);if(it != words.end())lexRes[lexI++] = make_pair(words[word], word);// cout << "(" << words[word] << "," << word << ")" << endl; elselexRes[lexI++] = make_pair("ident", word);// cout << "(ident" << "," << word << ")" << endl;i--;}// 常数else if(isdigit(inputs[i])){// 拿出常数word=inputs[i++];while(isdigit(inputs[i]))word+=inputs[i++];lexRes[lexI++] = make_pair("number", word);//cout << "(number" << "," << word << ")" << endl;i--;}// <、<=号else if(inputs[i]=='<'){word=inputs[i++];if(inputs[i]=='>'){word+=inputs[i];lexRes[lexI++] = make_pair(words[word], word);// cout << "(" << words[word] << "," << word << ")" << endl; }else if(inputs[i]=='='){word+=inputs[i];lexRes[lexI++] = make_pair(words[word], word);// cout << "(" <<words[word] << "," << word << ")" << endl; }else if(inputs[i]!=' '||!isdigit(inputs[i])||!isalpha(inputs[i])){lexRes[lexI++] = make_pair(words[word], word);// cout << "(" << words[word] << "," << word << ")" << endl; }else{//cout << "error!" << endl;}i--;}// >、>=else if(inputs[i]=='>'){word=inputs[i++];if(inputs[i]=='='){word+=inputs[i];lexRes[lexI++] = make_pair(words[word], word);// cout<<"("<<words[word]<<","<<word<<")"<<endl;}else if(inputs[i]!=' '||!isdigit(inputs[i])||!isalpha(inputs[i])){lexRes[lexI++] = make_pair(words[word], word);// cout<<"("<<words[word]<<","<<word<<")"<<endl;}else{//cout<<"error!"<<endl;}i--;}//:=else if(inputs[i]==':'){word=inputs[i++];if(inputs[i]=='='){word+=inputs[i];lexRes[lexI++] = make_pair(words[word], word);// cout<<"("<<words[word]<<","<<word<<")"<<endl;}else{//cout<<"error!"<<endl;}//i--;}//其他的基本字word=inputs[i];it=words.find(word);if(it!=words.end()){lexRes[lexI++] = make_pair(words[word], word);// cout<<"("<<words[word]<<","<<word<<")"<<endl; }else{//cout<<"error!"<<endl;}}}}/**四元式相关，被调⽤**/struct quad{string result;string arg1;string arg2;string op;};struct quad quad[50]; // 四元式数组int quaI = 0; // 指向四元式的指针void emit(string op, string arg1, string arg2, string result)/*发射⼀⾏四元式*/{quad[quaI].op = op;quad[quaI].arg1 = arg1;quad[quaI].arg2 = arg2;quad[quaI].result = result;quaI++;}int tI = 1; // 记录当前是t1/t2...t⼏了string newT()/*产⽣⼀个t1/t2...*/{stringstream ss;ss << tI;string ti = "t" + ss.str();tI++;return ti;}/**⾮算数表达式的递归下降分析及四元式⽣成**/// 指针前进int sym=0; // 正在处理的单词void advance(){++sym;if(sym > lexI){cout << "ERROR!sym指针越界";exit(0);}}string E();string T();string F();string F()/*因⼦分析*/{string arg;if(lexRes[sym].first == "ident"){arg = lexRes[sym].second;advance();}else if(lexRes[sym].first == "number"){arg = lexRes[sym].second;advance();}else if(lexRes[sym].first == "lparen"){advance();arg = E();if(lexRes[sym].first == "rparen"){advance();}else{cout << "ERROR!未能匹配右括号！语法错误\n";exit(0);}}}string T()/*项分析*/{string op, arg1, arg2, result;arg1 = F();while(lexRes[sym].first == "times" || lexRes[sym].first == "slash"){ op = lexRes[sym].second;advance();arg2 = F();result = newT();emit(op, arg1, arg2, result);arg1 = result;}return arg1;}string E()/*表达式分析*/{string op, arg1, arg2, result;if(lexRes[sym].first == "plus" || lexRes[sym].first == "minus"){advance();}arg1 = T();while(lexRes[sym].first == "plus" || lexRes[sym].first == "minus"){ op = lexRes[sym].second;advance();arg2 = T();result = newT();emit(op, arg1, arg2, result);arg1 = result;}return arg1;}/**算数表达式的递归下降分析及四元式⽣成**/int E_();int T_();int F_();int F_(){int arg;if(lexRes[sym].first == "ident"){cout << "算数表达式含变量，⽆法计算\n";exit(0);}else if(lexRes[sym].first == "number"){arg = atoi(lexRes[sym].second.c_str());advance();}else if(lexRes[sym].first == "lparen"){advance();arg = E_();if(lexRes[sym].first == "rparen"){advance();}else{cout << "ERROR!未能匹配右括号！语法错误\n";exit(0);}}return arg;}int T_()/*项分析*/{string op;int arg1, arg2, result;arg1 = F_();while(lexRes[sym].first == "times" || lexRes[sym].first == "slash"){ op = lexRes[sym].second;advance();arg2 = F_();if(op == "*"){result = arg1 * arg2;arg1 = result;}else{result = arg1 / arg2;arg1 = result;}else {cout << "除数为0，出错！\n";exit(0);}}}return arg1;}int E_()/*表达式分析*/{string op;int arg1, arg2, result;if(lexRes[sym].first == "plus" || lexRes[sym].first == "minus"){advance();}arg1 = T_();while(lexRes[sym].first == "plus" || lexRes[sym].first == "minus"){op = lexRes[sym].second;advance();arg2 = T_();if(op == "+"){result = arg1 + arg2;arg1 = result;}else{result = arg1 - arg2;arg1 = result;}}return arg1;}int main(){lexical();if(lexRes[0].first == "number"){cout << E_();}else{E();for(int i=0; i<quaI; i++){cout<<'('<<quad[i].op<<','<<quad[i].arg1<<','<<quad[i].arg2<<','<<quad[i].result<<')'<<endl; }}return 0;}。
