简单词法分析程序
编译原理课程词法分析程序，自己c++写的比较简单功能实现，需要的用户可以在此基础上进行自己思路的扩充修改。功能：读取一个自己设定路径下的txt文件中代码，然后将分析结果保存在另外一个自己设定路径下txt文件中，下附加代码：
/*
Name: 词法分析器
Copyright:
Author: ycc
Date: 24/03/17 11:24
Description: 词法分析器用于读取txt文本，其中每一个不同的单词都必须以空格隔开
*/
#include<iostream>
#include<fstream>
using namespace std;
int main()
{
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);//载入自己设定路径输入文件
ofstream outfile("C:/Users/Y/Desktop/old.txt",ios::out);//载入自己设定路径输出文件
for(i=0;i<200;i++)
{
a[i]=infile.get();//输入文件读取到数组a[]中
}
for(i=0;i<200;i++)//开始进行数组a[]内字符识别
{
switch(a[i])
{
case '('://识别符号（
{
b[j]=a[i];
outfile<<"<1,"<<b[j]<<">"<<endl;
} ;break;
case ')'://识别符号）
{
b[j]=a[i];
outfile<<"<2,"<<b[j]<<">"<<endl;
} ;break;
case '+':
{
if(a[i+1]=='=')//识别符号+=
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<3,"<<b[j]<<">"<<endl;
}
else if(a[i+1]=='+')//识别符号++
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<22,"<<b[j]<<">"<<endl;
}
else//识别符号+
{
b[j]+=a[i];
outfile<<"<4,"<<b[j]<<">"<<endl;
}
};break;
case '-':
{
if(a[i+1]=='=')//识别符号-=
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<5,"<<b[j]<<">"<<endl;
}
else if(a[i+1]=='-')//识别符号--
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<23,"<<b[j]<<">"<<endl;
}
else//识别符号-
{
b[j]+=a[i];
outfile<<"<6,"<<b[j]<<">"<<endl;
}
};break;
case '*':
{
if(a[i+1]=='=')//识别符号*=
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<7,"<<b[j]<<">"<<endl;
}
else//识别符号*
{
b[j]+=a[i];
outfile<<"<8,"<<b[j]<<">"<<endl;
}
};break;
case '/':
{
if(a[i+1]=='=')//识别符号 /=
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<9,"<<b[j]<<">"<<endl;
}
else if(a[i+1]=='/')////识别符号 //
{
while(a[i+2]!='\n')
{
i++;
}outfile<<"<10(1),"<<"注释"<<">"<<endl;
}
else////识别符号 /
{
b[j]+=a[i];
outfile<<"<10,"<<b[j]<<">"<<endl;
}
};break;
case ';'://识别符号 ；
{
b[j]=a[i];
outfile<<"<11,"<<b[j]<<">"<<endl;
};break;
case '<':
{
if(a[i+1]=='=')//识别符号<=
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<12,"<<b[j]<<">"<<endl;
}
else//识别符号 <
{
b[j]+=a[i];
outfile<<"<13,"<<b[j]<<">"<<endl;
}
};break;
case '>':
{
if(a[i+1]=='=')//识别符号 >=
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<14,"<<b[j]<<">"<<endl;
}
else//识别符号 >
{
b[j]+=a[i];
outfile<<"<15,"<<b[j]<<">"<<endl;
}
};break;
case '=':
{
if(a[i+1]=='=')//识别符号 ==
{
b[j]=a[i];
b[j]+=a[i+1];
i++;
outfile<<"<16,"<<b[j]<<">"<<endl;
}
else//识别符号 =
{
b[j]+=a[i];
outfile<<"<17,"<<b[j]<<">"<<endl;
}
};break;
}
if (a[i]==' '||a[i]=='\n') //识别符号空格及换行
{
j++;
}
if(a[i]>='0'&&a[i]<='9'||a[i]=='.')//识别小数及整数
{
b[j]+=a[i];
if(a[i+1]==' '||a[i+1]=='\n')//识别小数，下面语句进行位数控制
{
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') //关键字识别，自己添加需要的关键字
{
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;//识别自定义变量
}
}
if(a[i]==':')
{
if(a[i+1]=='=')//识别符号 :=
{
b[j]=a[i];
b[j]+=a[i+1];
outfile<<"<20,"<<b[j]<<">"<<endl;
i++;
}
else//识别符号 :
{
b[j]+=a[i];
outfile<<"<21,"<<b[j]<<">"<<endl;
}
}
}
cout<<"编译完毕"; //dos界面显示,则词法识别成功
outfile.close();//关闭文件
infile.close();//关闭文件
return 0;
}
结果显示效果如下（我是两个一起截图的）：
