编译原理：求非终结符的FOLLOW集合

来源：互联网发布：淘宝怎么发微淘编辑：程序博客网时间：2024/06/05 16:34
还是先把代码给贴出来，回头再找时间写篇文章总结一下，分析一下数据结构和算法
#pragma once#include <iostream>#include <algorithm>#include <fstream>#include <map>#include <set>#include <string>#include <stack>using namespace std;/*----------------------------------------全局变量存放终结符和非终结符---------------------------------------------------*/set<string> non_terminal;                                                       //存放非终结符set<string> productions;                                                        //存放产生式std::map<string, string> match_map;                                             //存放非终结符和其对应的产生式的文法的键值对std::map<string, set<string>> first;                                            //string:非终结符;set<string>:非终结符所对应的first集合std::map<string, set<string>> follow;                                           //string:非终结符;set<string>:非终结符所对应的follow集合bool is_not_changing = false;void divide_words(string grammar, map<string, string>& match_map) {    for (int i = 0; i < (int)grammar.length(); ++i) {        if (grammar[i] == '-' && grammar[i + 1] == '>') {            /* code */            string left = grammar.substr(0, i);                                 //一句文法的左边即非终结符            string right = grammar.substr(i + 2, grammar.length() - 1);         //一句文法的右边即非终结符对应的产生式            non_terminal.insert(left);                                          //插入非终结符集合里            productions.insert(right);                                          //插入产生式集合里            match_map.insert(make_pair(left, right));                           //将一句文法里的非终结符和其对应的产生式作为键值对插入到匹配map里            break;        }    }}/*将被'|'隔开的产生式拆分成对应多个的单词*/void divide_right(string grammar_right, set<string>& small_right) {    /*或许可以用grammar.find_first_of一个一个找|，然后用substr分开子串，最后再insert到small_right中去*/    size_t found = grammar_right.find('|');    if (found != string::npos) {        int i = 0;        string temp = "\0";        while ((size_t)i < grammar_right.length()) {            if (grammar_right[i] != '|') {                temp += grammar_right[i];                i = i + 1;            }            else {                i = i + 1;                small_right.insert(temp);                temp = "\0";            }            if (i == grammar_right.length()) {                small_right.insert(temp);                temp = "\0";            }        }    }    else {        small_right.insert(grammar_right);    }}/*对每个非终结符non_term寻找它的非终结符集合first*/void find_first(string non_term, set<string>& first) {    set<string> or_words;                                               //存放产生式中被'|'隔开的单词    auto search = match_map.find(non_term);    if (search != match_map.end()) {        divide_right(search->second, or_words);        //匹配非终结符是否在or_words的开头        for (set<string>::iterator i = or_words.begin(); i != or_words.end(); i++) {            for (set<string>::iterator j = non_terminal.begin(); j != non_terminal.end(); j++) {                if ((*i).find(*j) == 0) {                               //在or_words[i]的开头找到了一个非终结符                                                                        //递归寻找非终结符j的first集合                    find_first((*j), first);                }                else {                                                  //在or_words[i]的开头如果没有找到非终结符，即终结符                    if ((*i)[0] >= 'a' && (*i)[0] <= 'z') {                        first.insert(*i);                    }                    switch ((*i)[0]) {                    case '(':                        first.insert(string("("));                        break;                    case ')':                        first.insert(string(")"));                        break;                    case '+':                        first.insert(string("+"));                        break;                    case '*':                        first.insert(string("*"));                        break;                    case '#':                        first.insert(string("#"));                        break;                    default:                                            //如果没有匹配到符号的话就把这个单词插入到first集合中                                                                        //first.insert(*i);                        break;                    }                    continue;                                           //找到之后跳出循环，避免进行多余的遍历浪费时间                }            }        }    }}//对非终结符的follow集进行初始化，开始符号的follow集初始化成{$}，其余的初始化成空集void initial_follow() {    for (set<string>::iterator i = non_terminal.begin(); i != non_terminal.end(); i++) {        if (i == non_terminal.begin()) {            set<string> startFollow;            startFollow.insert("$");            auto pair = make_pair(*i, startFollow);            follow.insert(pair);        }        set<string> temp_follow;        auto pair = make_pair(*i, temp_follow);        follow.insert(pair);    }}//判断一个非终结符的first集合中是不是含有空串#bool first_contains_null(set<string> &first) {    auto find = first.find("#");    if (find != first.end()) {        return true;    }    return false;}//判断一个字符串str是否是非终结符，如果是返回true,否则返回falsebool is_non_terminal(string str) {    auto find = non_terminal.find(str);    if (find != non_terminal.end()) {        return true;    }    return false;}bool is_letter(char a) {                                                        //是否是小写字母    if (a >= 'a' && a <= 'z') {        return true;    }    return false;}bool is_cap_letter(char a) {    return (a >= 'A' && a <= 'Z') ? true : false;}//返回一个产生式的右部str的最后一个终结符或者非终结符string find_last(string &str) {    if ("\0" == str) {        return "\0";    }    if ('\'' == str.at(str.size() - 1)) {        string s = str.substr(str.size() - 2, 2);        str = str.substr(0, str.size() - 2);        return s;    }    else if (is_letter( str.at(str.size() - 1) ) && is_letter( str.at( str.size() - 2) ) ) {        string s = str.substr(str.size() - 2, 2);        str = str.substr(0, str.size() - 2);        return s;    }    else {        string s = str.substr(str.size() - 1, 1);        str = str.substr(0, str.size() - 1);        return s;    }}int cal_follow_total_size() {                                                   //计算所有follow集合的总size    int total_size = 0;    for (map<string, set<string>>::iterator i = follow.begin(); i != follow.end(); i++) {        total_size += i->second.size();    }    return total_size;}void find_follow(std::map<string, set<string>>& Follow) {    while (!is_not_changing) {        int fomer_size = cal_follow_total_size();        for (std::map<string, string>::iterator i = match_map.begin(); i != match_map.end(); i++) {//对每一个产生式进行遍历            set<string> or_words;            string left = (*i).first;                                       //左边的非终结符A            string right = (*i).second;                                     //右边的产生式A->b1b2b3B...            divide_right(right, or_words);            for (set<string>::iterator j = or_words.begin(); j != or_words.end(); j++) {                set<string> temp = Follow.find(left)->second;                string str;                string word = *j;                for (; word != "\0"; ) {                    str = find_last(word);                    if (!is_non_terminal(str)) {                        //是终结符                        temp.clear();                        temp.insert(str);                    }                    else {                        for (set<string>::iterator k = temp.begin(); k != temp.end(); k++) {                            if ("#" != (*k)) {                                (Follow.find(str)->second).insert(*k);                            }                        }                        if (!first_contains_null(first.find(str)->second)) {                            temp = first.find(str)->second;                        }                        else {                            for (set<string>::iterator m = first.find(str)->second.begin(); m != first.find(str)->second.end(); m++) {                                temp.insert(*m);                            }                        }                    }                }            }        }        //判断是否发生变化        int latter_size = cal_follow_total_size();        is_not_changing = fomer_size == latter_size ? true : false;    }}int main() {    /*读取文法文件*/    const char* filename = "wenfa.txt";    ifstream inFile(filename);    if (!inFile) {        cout << "\nFiled to open file " << filename;        return -1;    }    string st = "\0";    char buf[100];    while (!inFile.eof()) {        inFile.getline(buf, 20);        st = buf;        if (strlen(buf) == 0 || st == "end") {            break;        }        divide_words(st, match_map);                                        //对每一行文法进行分析找出非终结符和对应的产生式    }    inFile.close();    /*遍历非终结符集合，为每个非终结符寻找first集合*/    for (set<string>::iterator i = non_terminal.begin(); i != non_terminal.end(); ++i) {        set<string> the_first;                                              //当前非终结符的first集合        find_first(*i, the_first);        first.insert(make_pair(*i, the_first));    }    cout << "非终结符" << "\t" << "First集合" << endl;    for (map<string, set<string>>::iterator i = first.begin(); i != first.end(); i++) {        cout << "-------------------------" << endl;        cout << i->first << "\t|\t";        cout << "{ ";        //倒序输出first集合中的元素与文法中出现的顺序保持一致        for (set<string>::reverse_iterator j = (i->second).rbegin(); j != (i->second).rend(); j++) {            cout << *j << ", ";        }        cout << "\b\b }";        cout << endl;    }    cout << endl;    initial_follow();    find_follow(follow);    cout << "非终结符" << "\t" << "Follow集合" << endl;    for (map<string, set<string>>::iterator i = follow.begin(); i != follow.end(); i++) {        cout << "------------------------------" << endl;        cout << i->first << "\t|\t";        cout << "{ ";        //倒序输出first集合中的元素与文法中出现的顺序保持一致        for (set<string>::reverse_iterator j = (i->second).rbegin(); j != (i->second).rend(); j++) {            cout << *j << ", ";        }        cout << "\b\b }";        cout << endl;    }    return 0;}
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