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
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/*************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;} |
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原文链接：https://blog.csdn.net/did_you/article/details/78634852
