手工编写简易词法分析器

编译原理的作业，使用C手工编写词法简易词法分析器。大概内容就是根据指定的关键字，分隔符和其他的变量等，

在输入的一段程序中，将关键字，分隔符和变量，运算符等分别区分开来放到一个二元组里面，并且说明是第几个。

这个应该是书写编译器的开始，起初感觉很复杂，但是看看Demo还是可以的，下面来看一下源代码。

/* lexical analyzer */

#include <stdio.h>
#include <ctype.h>
#include <malloc.h>
#include <stdlib.h>
#include <string.h>

#define NULL 0
#define MAX_KEY_NUM		10  
#define MAX_BORDER_NUM	6
#define MAX_ARITH_NUM	4   
#define MAX_RELATION_NUM	6
#define MAX_CONSTS_NUM	20
#define MAX_LABEL_NUM	20


FILE *fp;
char cbuffer;

char *key[MAX_KEY_NUM]={"if","else","for","while","do","return","break","continue","main","int"};
char *border[MAX_BORDER_NUM]={",",";","{","}","(",")"};
char *arithmetic[MAX_ARITH_NUM]={"+","-","*","/"};
char *relation[MAX_RELATION_NUM]={"<","<=","==",">=",">","="};

char *consts[MAX_CONSTS_NUM];
char *label[MAX_LABEL_NUM];

int constnum=0,labelnum=0;

//===============================================
int search(char searchchar[],int wordtype)
{
     int i=0;
     switch (wordtype) {
       case 1:
			for (i=0;i<MAX_KEY_NUM;i++)
			{
				if (strcmp(key[i],searchchar)==0)
					return(i+1);
			}
       case 2:
		   {for (i=0;i<MAX_BORDER_NUM;i++)
			{
				if (strcmp(border[i],searchchar)==0)
					return(i+1);
			}
			return(0);
	      }

       case 3:
		   {for (i=0;i<MAX_ARITH_NUM;i++)
			{
				if (strcmp(arithmetic[i],searchchar)==0)
				{
					return(i+1);
				}
			}
			return(0);
	      }

       case 4:
		   {for (i=0;i<MAX_RELATION_NUM;i++)
			{
				if (strcmp(relation[i],searchchar)==0)
				{
					return(i+1);
				}
			}
			return(0);
	      }

       case 5:
			{
			   for (i=0;i<constnum;i++)
				{
					if(constnum>0)
						if (strcmp(consts[i],searchchar)==0)
						{
							return(i+1);
						}
				}
				consts[i]=(char *)malloc(sizeof(searchchar));
				strcpy(consts[i],searchchar);
				constnum++;
				return(i+1);
			}

       case 6:
			{			  
				for (i=0;i<labelnum;i++)
				{
						if (strcmp(label[i],searchchar)==0)
						{
							return(i+1);
						}
				}
			
				label[i]=(char *)malloc(sizeof(searchchar));
				strcpy(label[i],searchchar);
				labelnum++;
				return(i+1);
			}
      } // end of switch
}


//===============================================
char alphaprocess(char buffer)
{
	int atype;
	int i=-1;
	char alphatp[20];

	while ((isalpha(buffer))||(isdigit(buffer)))
	{
		alphatp[++i]=buffer;
		buffer=fgetc(fp);
	}
	alphatp[i+1]='\0';
	
	if (atype=search(alphatp,1))
		printf("%s	(1,%d)\n",alphatp,atype);
	else
	{
		atype=search(alphatp,6);
		printf("%s	(6,%d)\n",alphatp,atype);
	}

	return(buffer);
}

//===============================================
char digitprocess(char buffer)
{
	int i=-1;
	char digittp[20];
	int dtype;
	while ((isdigit(buffer)))
	{
	    digittp[++i]=buffer;
	    buffer=fgetc(fp);
	}
	digittp[i+1]='\0';
	dtype=search(digittp,5);
	printf("%s	(5,%d)\n",digittp,dtype);
	return(buffer);
}

//===============================================
char otherprocess(char buffer)
{

      int i=-1;
      char othertp[20];
      int otype,otypetp;
      othertp[0]=buffer;
      othertp[1]='\0';
      if (otype=search(othertp,3))
	 {
	 printf("%s	(3,%d)\n",othertp,otype-1);
	 buffer=fgetc(fp);
	 goto out;
	 }

      if (otype=search(othertp,4))
	      {
	      buffer=fgetc(fp);
	      othertp[1]=buffer;
	      othertp[2]='\0';
	      if (otypetp=search(othertp,4))
		 {
		 printf("%s	(4,%d)\n",othertp,otypetp-1);
		 goto out;
		 }
	      else
		 othertp[1]='\0';
		 printf("%s	(4,%d)\n",othertp,otype-1);
		 goto out;
	      }

      if (buffer==':')
	      {
	      buffer=fgetc(fp);
	      if (buffer=='=')
		 printf(":= (2,2)\n");
		 buffer=fgetc(fp);
		 goto out;
	      }
	   else
	      {
	      if (otype=search(othertp,2))
		 {
		 printf("%s	(2,%d)\n",othertp,otype-1);
		 buffer=fgetc(fp);
		 goto out;
		 }
	      }

	  if ((buffer!='\n')&&(buffer!=' '))
		  printf("%c error,not a word\n",buffer);
	  buffer=fgetc(fp);
out:      return(buffer);
}


//===============================================
void main()
{
	int i;

	for (i=0;i<=20;i++)
	{
	   label[i]=NULL;
	   consts[i]=NULL;
	};

	if ((fp=fopen("c:\example.c","r"))==NULL)
		printf("error");
	else
	{
		cbuffer = fgetc(fp);
		while (cbuffer!=EOF)
		{
			if (isalpha(cbuffer))
				cbuffer=alphaprocess(cbuffer);
			else if (isdigit(cbuffer))
				cbuffer=digitprocess(cbuffer);
			else cbuffer=otherprocess(cbuffer);
		}
		printf("over\n");
		getchar();
	 }
}

这样就算完成了。