C++实现词法分析器

本文实例为大家分享了C++实现词法分析器的具体代码，供大家参考，具体内容如下

 /*************Written By Zzg************/
      /*******Date : 11,25,2017********/
 
#include <iostream>
#include <stdlib.h>
#include <stdio.h>
 
using namespace std;
string KEYWORD[15]={"if","else","void","return","while","then","for","do",   //关键字
          "int","char","double","float","case","cin","cout"};
char SEPARATER[8]={';',',','{','}','[',']','(',')'};  //分隔符
char OPERATOR[8]={'+','-','*','/','>','<','=','!'};   //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<15;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<8;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<8;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){
  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,15,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,8,*arr.data()));
        cout<<arr<<" 运算符"<<endl;
        break;
      }
    case ';':
    case ',':
    case '(':
    case ')':
    case '[':
    case ']':
    case '{':
    case '}':
      {
       arr += ch;
       printf("%3d  ",value(SEPARATER,8,*arr.data()));
       cout<<arr<<" 分隔符"<<endl;
       break;
      }
    default :cout<<"\""<<ch<<"\":无法识别的字符！"<<endl;
    }
  }
 
}
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;
}

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持猪先飞。