C++实现词法分析器（学习）

我不是女神ヾ 2022-05-27 10:35 302阅读 0赞

参考网上程序，我把生成的数据存在文件里，能分析C语言的源程序

#include<fstream>  
    #include <iostream>  
    #include <stdlib.h>  
    #include <stdio.h>  
    using namespace std;  
    string KEYWORD[17]={
       "if","else","void","return","while","struct","for","do","int", //关键字 
                        "char","double","float","case","sizeof","break","swicth","default"};  
    char SEPARATER[10]={
       ';',',','{','}','[',']','(',')','"','#'};    //分隔符 
    char OPERATOR[11]={
       '+','-','*','/','>','<','=','!','%',':','?'};     //运算符 
    char FILTER[4]={
       ' ','\t','\r','\n'};                    //过滤符 
    const int IDENTIFIER=100;         //标识符值 
    const int CONSTANT=101;           //常数值 
    const int FILTER_VALUE=102;       //过滤字符值 
    
    
    /**判断是否为关键字**/  
    bool IsKeyword(string word){  
        for(int i=0;i<17;i++){  
            if(KEYWORD[i]==word){  
                return true;  
            }  
        }  
        return false;  
    }  
    /**判断是否为分隔符**/  
    bool IsSeparater(char ch){  
        for(int i=0;i<10;i++){  
            if(SEPARATER[i]==ch){  
                return true;  
            }  
        }  
        return false;  
    }  
    
    /**判断是否为运算符**/  
    bool IsOperator(char ch){  
        for(int i=0;i<11;i++){  
            if(OPERATOR[i]==ch){  
                return true;  
            }  
        }  
        return false;  
    }  
    /**判断是否为过滤符**/  
    bool IsFilter(char ch){  
        for(int i=0;i<4;i++){  
            if(FILTER[i]==ch){  
                return true;  
            }  
        }  
        return false;  
    }  
    /**判断是否为大写字母**/  
    bool IsUpLetter(char ch){  
        if(ch>='A' && ch<='Z') return true;  
        return false;  
    }  
    /**判断是否为小写字母**/  
    bool IsLowLetter(char ch){  
        if(ch>='a' && ch<='z') return true;  
        return false;  
    }  
    /**判断是否为数字**/  
    bool IsDigit(char ch){  
        if(ch>='0' && ch<='9') return true;  
        return false;  
    }  
    /**返回每个字的值**/  
    template <class T>  
    int value(T *a,int n,T str){  
        for(int i=0;i<n;i++){  
            if(a[i]==str) return i+1;  
        }  
        return -1;  
    }  
    /**词法分析**/  
    void analyse(FILE * fpin){  
        ofstream fout("out.txt");
        char ch=' ';  
        string arr="";  
        while((ch=fgetc(fpin))!=EOF)
        {  
            arr="";  
            if(IsFilter(ch))   {}              //判断是否为过滤符 
            else if(IsLowLetter(ch))
            {       //判断是否为关键字 
                while(IsLowLetter(ch))
                {  
                    arr += ch;  
                    ch=fgetc(fpin);  
                }  
                //fseek(fpin,-1L,SEEK_CUR); 
                if(IsKeyword(arr))
                {  
                    printf("%3d ",value(KEYWORD,17,arr));  
                    cout<<arr<<" 关键字"<<endl;  
                    fout<<"<"<<value(KEYWORD,17,arr)<<" "<<arr<<" "<<"关键字>\n";
                }  
                else  
                {  
                    printf("%3d ",IDENTIFIER);  
                    cout<<arr<<" 标识符"<<endl;  
                    fout<<"<"<<IDENTIFIER<<" "<<arr<<" "<<"标识符>\n";
                }  
            }  
            else if(IsDigit(ch))
            {           //判断是否为数字 
                while(IsDigit(ch)||(ch=='.'&&IsDigit(fgetc(fpin))))
                {  
                    arr += ch;  
                    ch=fgetc(fpin);  
                }  
                fseek(fpin,-1L,SEEK_CUR);  
                printf("%3d ",CONSTANT);  
                cout<<arr<<" 整形数"<<endl; 
                fout<<"<"<<CONSTANT<<" "<<arr<<" "<<"整形数>\n"; 
            }  
            else if(IsUpLetter(ch)||IsLowLetter(ch)||ch=='_')
            {  
                while(IsUpLetter(ch)||IsLowLetter(ch)||ch=='_'||IsDigit(ch))
                {  
                    arr += ch;  
                    ch=fgetc(fpin);  
                }  
                fseek(fpin,-1L,SEEK_CUR);  
                printf("%3d ",CONSTANT);  
                cout<<arr<<" 标识符"<<endl;  
                fout<<"<"<<CONSTANT<<" "<<arr<<" "<<"标识符>\n"; 
            }  
            else switch(ch)
            {  
            case '+':  
            case '-':  
            case '*':  
            case '/':  
            case '>':  
            case '<':  
            case '=':  
            case '!':  
            case ':':  
            case '?':  
            case '%':  
                {  
                    arr += ch;  
                    printf("%3d ",value(OPERATOR,11,*arr.data()));  
                    cout<<arr<<" 运算符"<<endl;  
                    fout<<"<"<<value(OPERATOR,11,*arr.data())<<" "<<arr<<" "<<"运算符>\n"; 
                    break;  
                }  
            case ';':  
            case ',':  
            case '(':  
            case ')':  
            case '[':  
            case ']':  
            case '{':  
            case '}':  
            case '"':  
            case '#':  
                {  
                  arr += ch;  
                  printf("%3d ",value(SEPARATER,10,*arr.data()));  
                  cout<<arr<<" 分隔符"<<endl;  
                 fout<<"<"<<value(SEPARATER,10,*arr.data())<<" "<<arr<<" "<<"分隔符>\n"; 
                  break;  
                }  
            default :
            {
                 arr += ch;  
            cout<<"\""<<arr<<"\":无法识别的字符！\n"<<endl; 
            fout<<"<无法识别的字符！>\n"; 
            } 
            }  
    
        }  
      fout.close();
    }  
    int main()  
    {  
        char inFile[40];  
        FILE *fpin;  
        cout<<"请输入源文件名（包括路径和后缀）:";  
        while(true){  
            cin>>inFile;  
            if((fpin=fopen(inFile,"r"))!=NULL)  
                break;  
            else{  
                cout<<"文件名错误！"<<endl;  
                cout<<"请输入源文件名（包括路径和后缀）:";  
            }  
    
        }  
        cout<<"------词法分析如下------"<<endl;  
        analyse(fpin);  
        return 0;  
    }