C++实现词法分析器

 #include <iostream>
 #include <stdlib.h>
 #include <stdio.h>

 using namespace std;
 string KEYWORD[]={"if","else","void","return","while","then","for","do",   //关键字
           "int","char","double","float","case","cin","cout"};
 char SEPARATER[]={';',',','{','}','[',']','(',')'};  //分隔符
 char OPERATOR[]={'+','-','*','/','>','<','=','!'};   //运算符
 char FILTER[]={' ','\t','\r','\n'};          //过滤符
 const int IDENTIFIER=;     //标识符值
 const int CONSTANT=;      //常数值
 const int FILTER_VALUE=;    //过滤字符值

 /**判断是否为关键字**/
 bool IsKeyword(string word){
   for(int i=;i<;i++){
     if(KEYWORD[i]==word){
       return true;
     }
   }
   return false;
 }
 /**判断是否为分隔符**/
 bool IsSeparater(char ch){
   for(int i=;i<;i++){
     if(SEPARATER[i]==ch){
       return true;
     }
   }
   return false;
 }

 /**判断是否为运算符**/
 bool IsOperator(char ch){
   for(int i=;i<;i++){
     if(OPERATOR[i]==ch){
       return true;
     }
   }
   return false;
 }
 /**判断是否为过滤符**/
 bool IsFilter(char ch){
   for(int i=;i<;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>='' && ch<='') 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=;i<n;i++){
  if(a[i]==str) return i+;
  }
  return -;
 }
 /**词法分析**/
 void analyse(FILE * fpin){
   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,,arr));
   cout<<arr<<" 关键字"<<endl;
   }
   else
       {
         printf("%3d  ",IDENTIFIER);
         cout<<arr<<" 标识符"<<endl;
       }
     }
     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;
     }
     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;
     }
     else switch(ch){
     case '+':
     case '-':
     case '*':
     case '/':
     case '>':
     case '<':
     case '=':
     case '!':
       {
         arr += ch;
         printf("%3d  ",value(OPERATOR,,*arr.data()));
         cout<<arr<<" 运算符"<<endl;
         break;
       }
     case ';':
     case ',':
     case '(':
     case ')':
     case '[':
     case ']':
     case '{':
     case '}':
       {
        arr += ch;
        printf("%3d  ",value(SEPARATER,,*arr.data()));
        cout<<arr<<" 分隔符"<<endl;
        break;
       }
     default :cout<<"\""<<ch<<"\":无法识别的字符！"<<endl;
     }
   }

 }
 int main()
 {
   char inFile[];
   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 ;
 }