1 #include <iostream>
  2 #include <stdlib.h>
  3 #include <stdio.h>
  4   
  5 using namespace std;
  6 string KEYWORD[15]={"if","else","void","return","while","then","for","do",   //關鍵字
  7           "int","char","double","float","case","cin","cout"};
  8 char SEPARATER[8
 
]={‘;‘,‘,‘,‘{‘,‘}‘,‘[‘,‘]‘,‘(‘,‘)‘};  //分隔符
  9 char OPERATOR[8]={‘+‘,‘-‘,‘*‘,‘/‘,‘>‘,‘<‘,‘=‘,‘!‘};   //運算符
 10 char FILTER[4]={‘ ‘,‘\t‘,‘\r‘,‘\n‘};          //過濾符
 11 const int IDENTIFIER=100;     //標識符值
 12 const int CONSTANT=101;      //常數值
 13 const int FILTER_VALUE=102;    //過濾字符值
 14   
 15   
 16
 
 /**判斷是否為關鍵字**/
 17 bool IsKeyword(string word){
 18   for(int i=0;i<15;i++){
 19     if(KEYWORD[i]==word){
 20       return true;
 21     }
 22   }
 23   return false;
 24 }
 25 /**判斷是否為分隔符**/
 26 bool IsSeparater(char ch){
 27   for(int i=0;i<8;i++){
 28     if(SEPARATER[i]==ch){
 29       return
 
 true;
 30     }
 31   }
 32   return false;
 33 }
 34   
 35 /**判斷是否為運算符**/
 36 bool IsOperator(char ch){
 37   for(int i=0;i<8;i++){
 38     if(OPERATOR[i]==ch){
 39       return true;
 40     }
 41   }
 42   return false;
 43 }
 44 /**判斷是否為過濾符**/
 45 bool IsFilter(char ch){
 46   for(int i=0;i<4;i++){
 47     if(FILTER[i]==ch){
 48       return true;
 49     }
 50   }
 51   return false;
 52 }
 53 /**判斷是否為大寫字母**/
 54 bool IsUpLetter(char ch){
 55   if(ch>=‘A‘ && ch<=‘Z‘) return true;
 56   return false;
 57 }
 58 /**判斷是否為小寫字母**/
 59 bool IsLowLetter(char ch){
 60   if(ch>=‘a‘ && ch<=‘z‘) return true;
 61   return false;
 62 }
 63 /**判斷是否為數字**/
 64 bool IsDigit(char ch){
 65   if(ch>=‘0‘ && ch<=‘9‘) return true;
 66   return false;
 67 }
 68 /**返回每個字的值**/
 69 template <class T>
 70 int value(T *a,int n,T str){
 71  for(int i=0;i<n;i++){
 72  if(a[i]==str) return i+1;
 73  }
 74  return -1;
 75 }
 76 /**詞法分析**/
 77 void analyse(FILE * fpin){
 78   char ch=‘ ‘;
 79   string arr="";
 80   while((ch=fgetc(fpin))!=EOF){
 81     arr="";
 82     if(IsFilter(ch)){}       //判斷是否為過濾符
 83     else if(IsLowLetter(ch)){    //判斷是否為關鍵字
 84       while(IsLowLetter(ch)){
 85   arr += ch;
 86   ch=fgetc(fpin);
 87       }
 88   //fseek(fpin,-1L,SEEK_CUR);
 89   if(IsKeyword(arr)){
 90         printf("%3d  ",value(KEYWORD,15,arr));
 91   cout<<arr<<" 關鍵字"<<endl;
 92   }
 93   else
 94       {
 95         printf("%3d  ",IDENTIFIER);
 96         cout<<arr<<" 標識符"<<endl;
 97       }
 98     }
 99     else if(IsDigit(ch)){      //判斷是否為數字
100       while(IsDigit(ch)||(ch==‘.‘&&IsDigit(fgetc(fpin)))){
101         arr += ch;
102         ch=fgetc(fpin);
103       }
104       fseek(fpin,-1L,SEEK_CUR);
105       printf("%3d  ",CONSTANT);
106       cout<<arr<<" 整形數"<<endl;
107     }
108     else if(IsUpLetter(ch)||IsLowLetter(ch)||ch==‘_‘){
109       while(IsUpLetter(ch)||IsLowLetter(ch)||ch==‘_‘||IsDigit(ch)){
110         arr += ch;
111         ch=fgetc(fpin);
112       }
113       fseek(fpin,-1L,SEEK_CUR);
114       printf("%3d  ",CONSTANT);
115       cout<<arr<<" 標識符"<<endl;
116     }
117     else switch(ch){
118     case ‘+‘:
119     case ‘-‘:
120     case ‘*‘:
121     case ‘/‘:
122     case ‘>‘:
123     case ‘<‘:
124     case ‘=‘:
125     case ‘!‘:
126       {
127         arr += ch;
128         printf("%3d  ",value(OPERATOR,8,*arr.data()));
129         cout<<arr<<" 運算符"<<endl;
130         break;
131       }
132     case ‘;‘:
133     case ‘,‘:
134     case ‘(‘:
135     case ‘)‘:
136     case ‘[‘:
137     case ‘]‘:
138     case ‘{‘:
139     case ‘}‘:
140       {
141        arr += ch;
142        printf("%3d  ",value(SEPARATER,8,*arr.data()));
143        cout<<arr<<" 分隔符"<<endl;
144        break;
145       }
146     default :cout<<"\""<<ch<<"\":無法識別的字符！"<<endl;
147     }
148   }
149   
150 }
151 int main()
152 {
153   char inFile[40];
154   FILE *fpin;
155   cout<<"請輸入源文件名（包括路徑和後綴）:";
156   while(true){
157     cin>>inFile;
158     if((fpin=fopen(inFile,"r"))!=NULL)
159       break;
160     else{
161       cout<<"文件名錯誤！"<<endl;
162       cout<<"請輸入源文件名（包括路徑和後綴）:";
163     }
164   
165   }
166   cout<<"------詞法分析如下------"<<endl;
167   analyse(fpin);
168   return 0;
169 }

C++實現詞法分析器