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

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