简单C语言词法分析器（C++实现）

た入场券 2022-06-07 03:52 631阅读 0赞

该程序实现了对C语言中变量、整数、符号及部分保留字的词法分析，下面给出各单词符号与种别码的对应关系。

1：保留字: int,double,char,if,else,for,while,do,return,break,continue,main  
2：变量：以下划线或字母开头的数字字母串，中间可混有下划线，例：\_abc1\_bcd  
3：整数：任意的数字串，程序可将其转化为对应的整型量  
4：运算符：+ - \* / = == > >= < <= !=  
5：分隔符：, ; :  
6：界符：( ) \[ \] \{ \} ‘ ‘ “ “

代码实现：  
*main.c*

#include <iostream>
    #include "LA.h"
    
    using namespace std;
    
    int main() {
        char *fn = "test.c";
        LA l(fn);
        l.show();
        l.scan();
        return 0;
    }

*LA.h*

#ifndef LEXICAL_ANALYZER_LA_H
    #define LEXICAL_ANALYZER_LA_H
    
    #include <iostream>
    #include <fstream>
    #include <sstream>
    #include <string>
    
    
    using namespace std;
    
    //保留字数组
    static string rsv_words[12] = {
       "int","double","char","if","else","for","while","do","return","break","continue","main"};
    
    class LA
    {
    private:
        ifstream fin;
        ostringstream sin;
        string txt; //存放读入的代码段
        string word; //存放构成单词的字符串
        int fg; //种别码
        int line; //记录行数
        int num; //存放整数
        char ch; //存放每次读入的字符
    public:
        void show(){
       cout<<txt<<endl;};
        LA(const char * s);
        void scan();
    };
    
    #endif //LEXICAL_ANALYZER_LA_H

*LA.cpp*

#include <iostream>
    #include "LA.h"
    
    using namespace std;
    
    LA::LA(const char * s):fin(s),line(1), num(0), fg(0), ch('\0')
    {
        sin <<fin.rdbuf();
        txt = sin.str();
        fin.close();
        fin.clear();
    }
    
    void LA::scan()
    {
        int p = 0;
    
        //读取第一个非空字符
        do{
            ch = txt[p++];
            if(ch == 10)
                line++;
        } while(ch == ' ' || ch == 10);
        cout<<"line "<<line<<" :"<<endl;
    
        while(ch != '\0'){
            while(ch == ' ' || ch == 10){
                if(ch == 10){
                    line++;
                    cout<<"line "<<line<<" :"<<endl;
                }
                ch = txt[p++];
            }
    
            //处理'_'开头的变量
            if(ch == '_'){
                word += ch;
                ch = txt[p++];
                if((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9')){
                    fg = 2;
                    word += ch;
                    ch = txt[p++];
                    while((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9') || ch == '_'){
                        word += ch;
                        ch = txt[p++];
                    }
                }
                else{
                    fg = -1;
                    word += ch;
                    ch = txt[p++];
                    while((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9') || ch == '_'){
                        word += ch;
                        ch = txt[p++];
                    }
                }
                switch(fg){
                    case -1: cout<<"error: "<<'<'<<word<<'>'<<endl; break;
                    case 2: cout<<'<'<<fg<<','<<word<<'>'<<endl; break;
                    default: break;
                }
                word.clear();
                fg = 0;
            }
    
            //处理保留字和字母开头的变量
            if((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')){
                fg = 1;
                word += ch;
                ch = txt[p++];
                while((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9') || ch == '_'){
                    word += ch;
                    ch = txt[p++];
                }
                for(int i = 0; i < 12; i++){
                    if(i == 11 && word != rsv_words[i])
                        fg++;
                    if(word == rsv_words[i]){
                        cout<<'<'<<fg<<','<<word<<'>'<<endl;
                        word.clear();
                        break;
                    }
                }
                if(fg == 2)
                    cout<<'<'<<fg<<','<<word<<'>'<<endl;
                word.clear();
                fg = 0;
            }
    
            //处理整数
            if(ch >= '0' && ch <= '9'){
                fg = 3;
                num = 10 * num + (ch - '0');
                ch = txt[p++];
                while(ch >= '0' && ch <= '9'){
                    num = 10 * num + (ch - '0');
                    ch = txt[p++];
                }
                cout<<'<'<<fg<<','<<num<<'>'<<endl;
                num = 0;
                fg = 0;
            }
    
            //处理符号
            switch(ch){
                //处理运算符
                case '+': fg = 4; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case '-': fg = 4; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case '*': fg = 4; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case '/': fg = 4; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case '=':
                    fg = 4;
                    if(txt[p] == '='){
                        word += ch;
                        ch = txt[p++];
                        word += ch;
                        ch = txt[p++];
                        cout<<'<'<<fg<<','<<word<<'>'<<endl;
                        word.clear();
                        break;
                    }
                    else{
                        cout<<'<'<<fg<<','<<ch<<'>'<<endl;
                        ch = txt[p++];
                        break;
                    }
                case '<':
                    fg = 4;
                    if(txt[p] == '='){
                        word += ch;
                        ch = txt[p++];
                        word += ch;
                        ch = txt[p++];
                        cout<<'<'<<fg<<','<<word<<'>'<<endl;
                        word.clear();
                        break;
                    }
                    else{
                        cout<<'<'<<fg<<','<<ch<<'>'<<endl;
                        ch = txt[p++];
                        break;
                    }
                case '>':
                    fg = 4;
                    if(txt[p] == '='){
                        word += ch;
                        ch = txt[p++];
                        word += ch;
                        ch = txt[p++];
                        cout<<'<'<<fg<<','<<word<<'>'<<endl;
                        word.clear();
                        break;
                    }
                    else{
                        cout<<'<'<<fg<<','<<ch<<'>'<<endl;
                        ch = txt[p++];
                        break;
                    }
                case '!':
                    fg = 4;
                    if(txt[p] == '='){
                        word += ch;
                        ch = txt[p++];
                        word += ch;
                        ch = txt[p++];
                        cout<<'<'<<fg<<','<<word<<'>'<<endl;
                        word.clear();
                        break;
                    }
                    else{
                        cout<<'<'<<fg<<','<<ch<<'>'<<endl;
                        ch = txt[p++];
                        break;
                    }
    
                //处理分隔符
                case ',': fg = 5; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case ';': fg = 5; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case ':': fg = 5; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
    
                //处理界符
                case '(': fg = 6; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case ')': fg = 6; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case '[': fg = 6; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case ']': fg = 6; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case '{': fg = 6; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case '}': fg = 6; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case '"': fg = 6; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
                case '\'': fg = 6; cout<<'<'<<fg<<','<<ch<<'>'<<endl; ch = txt[p++]; break;
            }
        }
    
    
    }

*测试文件 test.c*

int main()
    {
        int __ab12_asd23;
        int _a1 = 001, b2 = 12, abc_def;
        for(int i = 0; i <= 10; i++) {
            _a1 += b2;
            if(_a1 == 37)
                break;
            else
                continue;
        }
        return 0;
    }