simple lexical analyzer
Compilation principle course lexical analysis program, written in C++ with relatively simple function implementation, users who need it can expand and modify their own ideas on this basis. Function: Read the code in a txt file under the path set by yourself , and then save the analysis results in another txt file under the path set by yourself , and add the following code:
/*
Name: Lexical Analyzer
Copyright:
Author: ycc
Date: 24/03/17 11:24
Description: The lexical analyzer is used to read txt text, where each distinct word must be separated by spaces
*/
#include<iostream>
#include<fstream>
using namespace std;
intmain()
{
char a[200];
string b[200];
static int j=0;
int i;
int count;
int flag;
ifstream infile("C:/Users/Y/Desktop/new.txt ",ios::in);//Load the input file with your own set path
ofstream outfile("C:/Users/Y/Desktop/old.txt",ios::out);//Load the output file with your own set path
for(i=0;i<200;i++)
{
a[i]=infile.get();//The input file is read into the array a[]
}
for(i=0;i<200;i++)//Start character recognition in array a[]
{
switch(a[i])
{
case '('://Identifier (
{
b[j]=a[i];
outfile<<"<1,"<<b[j]<<">"<<endl;
} ;break;
case ')'://identifier)
{
b[j]=a[i];
outfile<<"<2,"<<b[j]<<">"<<endl;
} ;break;
case '+':
{
if(a[i+1]=='=')//Identifier+=
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<3,"<<b[j]<<">"<<endl;
}
else if(a[i+1]=='+')//Identifier++
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<22,"<<b[j]<<">"<<endl;
}
else//Identifier+
{
b[j]+=a[i];
outfile<<"<4,"<<b[j]<<">"<<endl;
}
};break;
case '-':
{
if(a[i+1]=='=')//Identifier-=
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<5,"<<b[j]<<">"<<endl;
}
else if(a[i+1]=='-')//Identifier--
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<23,"<<b[j]<<">"<<endl;
}
else//Identifier-
{
b[j]+=a[i];
outfile<<"<6,"<<b[j]<<">"<<endl;
}
};break;
case '*':
{
if(a[i+1]=='=')//Identifier*=
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<7,"<<b[j]<<">"<<endl;
}
else//Identifier*
{
b[j]+=a[i];
outfile<<"<8,"<<b[j]<<">"<<endl;
}
};break;
case '/':
{
if(a[i+1]=='=')//Identifier/=
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<9,"<<b[j]<<">"<<endl;
}
else if(a[i+1]=='/')////Identifier//
{
while(a[i+2]!='\n')
{
i++;
}outfile<<"<10(1),"<<"注释"<<">"<<endl;
}
else////Identifier/
{
b[j]+=a[i];
outfile<<"<10,"<<b[j]<<">"<<endl;
}
};break;
case ';'://identifier;
{
b[j]=a[i];
outfile<<"<11,"<<b[j]<<">"<<endl;
};break;
case '<':
{
if(a[i+1]=='=')//Identifier<=
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<12,"<<b[j]<<">"<<endl;
}
else//Identifier<
{
b[j]+=a[i];
outfile<<"<13,"<<b[j]<<">"<<endl;
}
};break;
case '>':
{
if(a[i+1]=='=')//Identifier>=
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<14,"<<b[j]<<">"<<endl;
}
else//identifier>
{
b[j]+=a[i];
outfile<<"<15,"<<b[j]<<">"<<endl;
}
};break;
case '=':
{
if(a[i+1]=='=')//Identifier==
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<16,"<<b[j]<<">"<<endl;
}
else//Identifier =
{
b[j]+=a[i];
outfile<<"<17,"<<b[j]<<">"<<endl;
}
};break;
}
if (a[i]==' '||a[i]=='\n') //Identifier spaces and newlines
{
j++;
}
if(a[i]>='0'&&a[i]<='9'||a[i]=='.')//Identify decimals and integers
{
b[j]+=a[i];
if(a[i+1]==' '||a[i+1]=='\n')//Identify decimals, the following statement controls the number of digits
{
if(a[i-1]=='.'||a[i-2]=='.'||a[i-3]=='.'||a[i-4]=='.'||a[i-5]=='.'||a[i-6]=='.')
outfile<<"<18(1),"<<b[j]<<">"<<endl;
else
outfile<<"<18,"<<b[j]<<">"<<endl;//识别整数
}
}
if(a[i]>='a'&&a[i]<='z') //Keyword identification, add the required keywords yourself
{
b[j]+=a[i];
if(a[i+1]==' '||a[i+1]=='\n')
{
if(b[j]=="while")
outfile<<"<19(1),"<<b[j]<<">"<<endl;
else if(b[j]=="int")
outfile<<"<19(2),"<<b[j]<<">"<<endl;
else if(b[j]=="float")
outfile<<"<19(3),"<<b[j]<<">"<<endl;
else if(b[j]=="do")
outfile<<"<19(4),"<<b[j]<<">"<<endl;
else if(b[j]=="public")
outfile<<"<19(5),"<<b[j]<<">"<<endl;
else if(b[j]=="void")
outfile<<"<19(6),"<<b[j]<<">"<<endl;
else if(b[j]=="if")
outfile<<"<19(7),"<<b[j]<<">"<<endl;
else
outfile<<"<19,"<<b[j]<<">"<<endl;//Identify custom variables
}
}
if(a[i]==':')
{
if(a[i+1]=='=')//Identifier:=
{
b[j]=a[i];
b[j]+=a[i+1];
outfile<<"<20,"<<b[j]<<">"<<endl;
i++;
}
else//Identifier :
{
b[j]+=a[i];
outfile<<"<21,"<<b[j]<<">"<<endl;
}
}
}
cout<<"Compilation completed"; //The dos interface is displayed, the lexical recognition is successful
outfile.close();//Close the file
infile.close();//Close the file
return 0;
}
The results are shown as follows (I took two screenshots together) :
