下面教大家用c++语言实现编译原理中的词法分析器。
一、运行说明：
1、电脑环境：win10+64位
2、编译软件：Dev-C++
3、将要分析的程序或字符以txt（文本）形式存在文件夹中（我分析的是qq.txt,下图是它的存储路径）
附：qq.txt
int main(){char inFile[40];FILE *fpin;analyse(fpin);return 0;}
4、编译运行
二、源代码
#include <iostream>#include <stdlib.h>#include <stdio.h>using**加粗样式** 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;}
三、运行截图
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