c语言实现词法分析器+文法分析器（全代码）
2024-06-07 12:29:11
学习记录，可能有很多不足，请谅解。
基本按照教材方法
注意本次词法分析只分析上图中拥有的
#include<iostream>
#include<string.h>
#include<stdio.h>
using namespace std;string reservewords[] = { "while","if","else","int","print"};//保留字
char character;//单个字符
string token;//一串字符
string yuyan;//语法分析结果
int numbers[9];//常量储存
int numberid = 0;
int wordsid = 0;
int boolflag;//储存id。转换。
int boolflag1;
int boolflag2;
bool elseflag=false;//判断else是否可执行
int whileflag=0;//判断while是否可执行
struct word
{string name;int value;
}words[9];//变量储存bool digit() {//是否为数字return character >= '0' && character <= '9' ? 1 : 0;
}void getbe() {//去除空格while (1) {if (character == ' ') {character = getchar();}else {break;}}
}bool letter() {//是否为字符return (character >= 'a' && character <= 'z') || (character >= 'A' && character <= 'Z') ? 1 : 0;
}void concatenation() {//连接字符串token = token + character;
}int reserve() {//判断是否为保留字int id = 0;for (auto s : reservewords) {id++;if (s==token) {return id;}}return 0;
}int word() {//判断变量是否存在int id = 0;for (int i = 0; i < 10;i++) {id++;string s = words[i].name;if (s==token) {return id;}}return 0;
}int number() {//判断常量是否存在for (int i = 0; i <= numberid;i++) {if (numbers[i]== atoi(token.c_str())) {return i+1;}}return 0;
}int main()
{freopen("chenxu.txt", "r", stdin);//读取土木character = getchar();while (character!=EOF) {//词法分析getbe();if (letter()) {while (letter() || digit()) {concatenation();character = getchar();}boolflag = reserve();if (boolflag!= 0) {yuyan += '_';yuyan += (boolflag + '0');token = "";}else {boolflag = word();if (boolflag != 0) {yuyan += '@';yuyan += (boolflag + '0');}else {words[wordsid].name= token;words[wordsid].value = 0;yuyan += '@';yuyan += ((wordsid+1) + '0');wordsid++;}token = "";}}else if (digit()) {while (digit()) {concatenation();character = getchar();}boolflag = number();if (boolflag != 0) {yuyan += '$';yuyan += (boolflag + '0');}else {int n = atoi(token.c_str());numbers[numberid] = n;yuyan += '$';yuyan += ((numberid + 1) + '0');numberid++;}token = "";}else if (character == '+') {yuyan += character;character = getchar();}else if (character == '-') {yuyan += character;character = getchar();}else if (character == '=') {yuyan += character;character = getchar();}else if (character == '>') {int flag = 0;character = getchar();if (character == '=') {flag = 1;yuyan += '>';yuyan += character;character = getchar();}if (flag == 0) {yuyan += '>';}}else if (character == '<') {yuyan += character;character = getchar();}else if (character == '(') {yuyan += character;character = getchar();}else if (character == ')') {yuyan += character;character = getchar();}else if (character == '{') {yuyan += character;character = getchar();}else if (character == '}') {yuyan += character;character = getchar();}else if (character == ';') {yuyan += character;character = getchar();}else {character = getchar();continue;}}cout << yuyan;cout << endl;
}
上面是词法分析，下为文法分析，因为文法分析当时只做到了能分析老师给的特定序列并输出结果，所以文法分析存在很多问题，1. if和else依然一对一匹配，但是if和else中间可以穿插其他语句。可以在程序中写判断大小的句子，作为中断判定，如果判断失败，则作为断点中断程序，如果判断成功，就继续程序。while中只能再出现while或一个计算式等
在代码中添加函数
int bds(int i) {//单个式子文法if (yuyan[i] == '@') {i++;character = yuyan[i];if (digit()) {boolflag = character - '0';i++;character = yuyan[i];if (character == '='){i++;character = yuyan[i];if (yuyan[i] == '@') {i++;character = yuyan[i];if (digit()) {boolflag1 = character - '0';i++;character = yuyan[i];if (character == '+'){i++;character = yuyan[i];if (yuyan[i] == '$') {i++;character = yuyan[i];if (digit()) {boolflag2 = character - '0';i++;character = yuyan[i];if (character == ';'){words[boolflag - 1].value = words[boolflag1 - 1].value + numbers[boolflag2 - 1];i++;return i;}else {return 0;}}else {return 0;}}else {return 0;}}else if (character == '-') {i++;character = yuyan[i];if (yuyan[i] == '$') {i++;character = yuyan[i];if (digit()) {boolflag2 = character - '0';i++;character = yuyan[i];if (character == ';'){words[boolflag - 1].value = words[boolflag1 - 1].value - numbers[boolflag2 - 1];i++;return i;}else {return 0;}}else {return 0;}}else {return 0;}}else {return 0;}}else {return 0;}}}else if (character == '>') {i++;character = yuyan[i];if (yuyan[i] == '$') {i++;character = yuyan[i];if (digit()) {boolflag1 = character - '0';if (words[boolflag - 1].value > numbers[boolflag1-1]) {i++;return i;}else {return -1;}}else {return 0;}}else if (character == '=') {i++;character = yuyan[i];if (yuyan[i] == '$') {i++;character = yuyan[i];if (digit()) {boolflag1 = character - '0';if (words[boolflag - 1].value >= numbers[boolflag1-1]) {i++;return i;}else {return -1;}}else {return 0;}}else {return 0;}}else {return 0;}}else if (character == '<') {i++;character = yuyan[i];if (yuyan[i] == '$') {i++;character = yuyan[i];if (digit()) {boolflag1 = character - '0';if (words[boolflag - 1].value < numbers[boolflag1-1]) {i++;return i;}else {return -1;}}else {return 0;}}else {return 0;}}else {return 0;}}else {return 0;}}else {return 0;}
}int whilesx(int i) {//循环分析int j = i;i++;int aa = bds(i);if (aa > 0) {i = aa;character = yuyan[i];if (character == ')') {i++;character = yuyan[i];if (character == '{') {i++;character = yuyan[i];aa = bds(i);if (aa != 0) {i = aa;if (yuyan[i] == '}') {i++;whileflag = i;i = j;whileflag=whilesx(i);}else {return 0;}}else {if (character == '_') {i++;character = yuyan[i];if (yuyan[i] == '1') {i++;character = yuyan[i];if (yuyan[i] == '(') {whileflag=whilesx(i);i = j;whileflag=whilesx(i);}else {return 0;}}else {return 0;}}else {return 0;}}}else {return 0;}}else {return 0;}}else if (aa == -1) {if (whileflag == 0) {while (yuyan[i] != '}') {i++;}whileflag = i;return whileflag;}else {return whileflag;}}else {return 0;}
}
在main方法中添加
for (int i = 0; i < yuyan.length();) {//文法分析，输出结果character = yuyan[i];if (character == '_') {i++;character = yuyan[i];if (character == '1') {i++;character = yuyan[i];if (yuyan[i] == '(') {int aa = whilesx(i);if (aa == 0) {cout << "出错了"; break;}else {while (yuyan[aa] == '}') {aa++;}i = aa;}}else {cout << "出错了"; break;}}else if (character == '2') {elseflag = false;i++;character = yuyan[i];if (yuyan[i] == '(') {i++;int aa = bds(i);if (aa > 0) {elseflag = false;i = aa;character = yuyan[i];if (character == ')') {i++;character = yuyan[i];if (character == '{') {i++;character = yuyan[i];aa = bds(i);if (aa != 0) {i = aa;if (yuyan[i] == '}') {i++;continue;}else {cout << "出错了"; break;}}else {cout << "出错了"; break;}}else {cout << "出错了"; break;}}else {cout << "出错了"; break;}}else if (aa == -1) {elseflag = true;while (yuyan[i] != '}') {i++;}i++;}else {cout << "出错了"; break;}}else {cout << "出错了"; break;}}else if (character == '3') {if (elseflag == false) {while (yuyan[i] != '}') {i++;}i++;}else {i++;character = yuyan[i];if (yuyan[i] == '{') {i++;character = yuyan[i];int aa = bds(i);if (aa != 0) {i = aa;if (yuyan[i] == '}') {i++;continue;}else {cout << "出错了"; break;}}else {cout << "出错了"; break;}}else {cout << "出错了"; break;}}}else if (character == '4') {i++;character = yuyan[i];if (yuyan[i] == '@') {i++;character = yuyan[i];if (digit()) {boolflag = character - '0';i++;character = yuyan[i];if (character == '='){i++;character = yuyan[i];if (yuyan[i] == '$') {i++;character = yuyan[i];if (digit()) {boolflag1 = character - '0';i++;character = yuyan[i];if (character == ';'){words[boolflag - 1].value = numbers[boolflag1 - 1];i++;}else {cout << "出错了";break;}}else {cout << "出错了";break;}}else {cout << "出错了";break;}}else {cout << "出错了";break;}}else {cout << "出错了";break;}}else {cout << "出错了";break;}}else if (character == '5') {i++;character = yuyan[i];if (yuyan[i] == '@') {i++;character = yuyan[i];if (digit()) {boolflag = character - '0';i++;character = yuyan[i];if (character == ';'){cout << words[boolflag - 1].value;i++;}else {cout << "出错了";break;}}else {cout << "出错了";break;}}else {cout << "出错了";break;}}else { cout << "出错了"; break; }}else if (character == '@') {i = bds(i);if (i == 0) {cout << "出错了"; break;}if(i==-1){cout << "程序中断退出"; break;}}else {cout << "出错了"; break;}}
结果展示
感谢观看
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