词法分析器.cpp

实验题目：词法分析器 一、实验目的： 设计、编制、调试一个词法分析子程序－识别单词

// Note:Your choice is C++ IDE
#include <iostream>

#include<string>

using namespace std;

#define  MAX 22          

char ch =' ';

string key[15]={"begin","end","if","then","else","while","write","read",

"do", "call","const","char","until","procedure","repeat"};

int Iskey(string c){         //关键字判断

   int i;

   for(i=0;i<MAX;i++) {

      if(key[i].compare(c)==0) return 1;

       } 

    return 0;

}

int IsLetter(char c) {        //判断是否为字母

    if(((c<='z')&&(c>='a'))||((c<='Z')&&(c>='A'))) return 1;

    else return 0;

}

int IsDigit(char c){          //判断是否为数字

     if(c>='0'&&c<='9') return 1;

     else return 0;

}

void analyse(FILE *fpin){

    string arr="";          

    while((ch=fgetc(fpin))!=EOF) {

            arr="";        

         if(ch==' '||ch=='\t'||ch=='\n'){}     

 

         else if(IsLetter(ch)){

                 while(IsLetter(ch)||IsDigit(ch)) {

                                if((ch<='Z')&&(ch>='A')) ch=ch+32;   

                             arr=arr+ch;

                    ch=fgetc(fpin);

                               }

                 fseek(fpin,-1L,SEEK_CUR);    

                 if (Iskey(arr)){cout<<arr<<"\t$关键字"<<endl;}     

                 else  cout<<arr<<"\t$普通标识符"<<endl;           

               }

      

            else if(IsDigit(ch)){

                  while(IsDigit(ch)||ch=='.'&&IsDigit(fgetc(fpin))){

                        arr=arr+ch;

                        ch=fgetc(fpin);

                       }

                  fseek(fpin,-1L,SEEK_CUR);

                  cout<<arr<<"\t$无符号实数"<<endl;  

             }

       else switch(ch){          

               case'+':

               case'-' :

               case'*' :

               case'=' :

               case'/' :cout<<ch<<"\t$运算符"<<endl;break;

               case'(' :

               case')' :

               case'[' :

               case']' :               

               case';' :

               case'.' :

               case',' :

               case'{' :

               case'}' :cout<<ch<<"\t$界符"<<endl;break;

               case':' :{ch=fgetc(fpin);

                        if(ch=='=') cout<<":="<<"\t$运算符"<<endl;

                        else {cout<<"="<<"\t$运算符"<<endl;;

                               fseek(fpin,-1L,SEEK_CUR);}

                        }break;

case'>' :{ch=fgetc(fpin);

                         if(ch=='=') cout<<">="<<"\t$运算符"<<endl;

                         if(ch=='>')cout<<">>"<<"\t$输入控制符"<<endl;

                         else {cout<<">"<<"\t$运算符"<<endl;

                             fseek(fpin,-1L,SEEK_CUR);}

                         }break;

               case'<' :{ch=fgetc(fpin);

                         if(ch=='=')cout<<"<="<<"\t$运算符"<<endl;

                         else if(ch=='<')cout<<"<<"<<"\t$输出控制符"<<endl;

                         else if(ch=='>') cout<<"<>"<<"\t$运算符"<<endl;

                         else{cout<<"<"<<"\t$运算符"<<endl;

                            fseek(fpin,-1L,SEEK_CUR);}

                        }break;

              default : cout<<ch<<"\t$无法识别字符"<<endl;

        }

    }

}

void main(){

   char in_fn[30];

   FILE * fpin;

   cout<<"请输入源文件名（包括路径和后缀名）:";

   for(;;){

       cin>>in_fn;

       if((fpin=fopen(in_fn,"r"))!=NULL) break;

       else cout<<"文件路径错误！请输入源文件名（包括路径和后缀名）:";

     }

   cout<<"\n********************分析如下*********************"<<endl;

   analyse(fpin);

   fclose(fpin);

}