简单的词法分析器

最新推荐文章于 2025-05-19 15:57:59 发布

cqnuztq

最新推荐文章于 2025-05-19 15:57:59 发布

阅读量929

点赞数

CC 4.0 BY-SA版权

分类专栏：其他文章标签： search fp null struct c

本文链接：https://blog.youkuaiyun.com/cqnuztq/article/details/4702587

其他专栏收录该内容

7 篇文章

订阅专栏

本文介绍了一个简单的C语言词法分析器实现，通过解析预定义关键字、操作符、比较符及标点符号来识别输入源文件中的词汇单元。该分析器能够处理包括关键字、数字、标识符等在内的多种词法元素。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

//#include "stdafx.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <malloc.h>
#include <ctype.h>
#include <conio.h>
#define NULL 0
FILE *fp;
char ch;
char *keyword[32]={"auto","break","case","char","const",
"continue","default","do","double","else","enum","extern",
"float","for","goto","if","int","long","register","return",
"short","signed","sizeof","static","struct","switch",
"typedef","union","unsigned","void","volatile","while"};
char *operatornum[5]={"+","-","*","/","%"};
char *comparison[6]={"<","<=","==",">",">=","<>"};
char *interpunction[6]={",",";","=",".","(",")"};

////////////////////////////////////////////////////////////////////////
bool search(char searchstr[],int wordtype)
{
int i;
switch (wordtype)
{
case 1:for(i=0;i<=31;i++)
     {
      if(strcmp(keyword[i],searchstr)==0)
       return(true);

     }
case 2:{
for(i=0;i<=4;i++)
{
   if(strcmp(operatornum[i],searchstr)==0)
    return(true);
}
break;
     }
case 3: for(i=0;i<=5;i++)
   {
    if(strcmp(comparison[i],searchstr)==0)
     return(true);
   }
case 4: for(i=0;i<=5;i++)
   {
    if(strcmp(interpunction[i],searchstr)==0)
     return(true);
   }

}
return(false);
}

///////////////////////////////////////////////////////////////////////////////////////////

char letterprocess (char ch)//字母处理函数
{
int i=-1;
char letter[20];
while (isalnum(ch)!=0) //如果本函数的变元为字母或数字，它将返回非零值，否则返回零值
{
letter[++i]=ch;
ch=fgetc(fp);
};
letter[i+1]='/0';
if (search(letter,1))
{
printf("<%s,->/n",letter);
//strcat(letter,"/n");
//fputs('<' letter '>/n',outp);
}
else
{
printf("<indentifier,%s>/n",letter);
//strcat(letter,"/n");
//fputs(letter,outp);
}
return(ch);
}
////////////////////////////////////////////////////////////////////////////////////////

char numberprocess(char ch)     //数字处理程序
{
int i=-1;
char num[20];
while (isdigit(ch)!=0)
{
num[++i]=ch;
ch=fgetc(fp);
}
/* if(isalpha(ch)!=0)
{
while(isspace(ch)==0)
{
   num[++i]=ch;
            ch=fgetc(fp);
}
num[i+1]='/0';
printf("错误！非法标识符：%s/n",num);
goto u;
}*/
num[i+1]='/0';
    printf("<num,%s>/n",num);
    //strcat(num,"/n");
    //fputs(num,outp);
    //u: return(ch);
return(ch);
}

//////////////////////////////////////////////////////////////////////////////////////////////

char otherprocess(char ch)
{
int i=-1;
char other[20];
if (isspace(ch)!=0)
{
ch=fgetc(fp);
goto u;
}
while ((isspace(ch)==0)&&(isalnum(ch)==0))
{
other[++i]=ch;
ch=fgetc(fp);
}
other[i+1]='/0';
if (search(other,2))
printf("<relop,%s>/n",other);
else
if (search(other,3))
   printf("<%s,->/n",other);
else
   if (search(other,4))
    printf("<%s,->/n",other);
   else
    printf("错误！非法字符：%s/n",other);
u: return (ch);
}

/////////////////////////////////////////////////////////////////////////////////////////////
void main ()
{
char str,c;
printf("**********************************词法分析器************************************/n");
//outp=fopen("二元式表.txt","w");
if ((fp=fopen("源程序.txt","r"))==NULL)
printf("源程序无法打开！/n");
else
{
str =fgetc(fp);
while (str!=EOF)
{
   if (isalpha(str)!=0)    //判断字符c是否为英文字母，当c为英文字母a-z或A-Z时，在标准c中相当于使用“isupper(c)||islower(c)”做测试，返回非零值，否则返回零。
    str=letterprocess(str);
   else
   {
    if (isdigit(str)!=0) //判断字符c是否为数字,当c为数字0-9时，返回非零值，否则返回零
     str=numberprocess(str);
    else
     str=otherprocess(str);
   }

};
printf("词法分析结束，谢谢使用!/n");
printf("点任意键退出!/n");
}
   c=getch();
}