实验一、词法分析实验

一、 实验目的

通过设计一个词法分析程序，对词法进行分析，加强对词法的理解，掌握对程序设计语言的分解和理解。

二、 实验内容和要求

在原程序中输入源代码

• 对字符串表示的源程序
• 从左到右进行扫描和分解
• 根据词法规则
• 识别出一个一个具有独立意义的单词符号
• 以供语法分析之用
• 发现词法错误，则返回出错信息

在源程序中，自动识别单词，把单词分为五种，并输出对应的单词种别码。

1. 识别关键字：main if int for while do return break continue，该类的单词码为1.
2. 识别标识符：表示各种名字，如变量名、数组名、函数名等，如char ch, int syn, token,sum，该类的单词码为2.
3. 运算符：+、-、*、/、=、>、<、>=、<=、!=
4. 分隔符：,、;、{、}、(、)
5. 常数，例：123

各种单词符号对应的种别码。

输出形式：

• 二元式

– （单词种别，单词自身的值）

• 单词种别，表明单词的种类，语法分析需要的重要信息

– 整数码

• 关键字、运算符、界符：一符一码
• 标识符：10, 常数：11
• 单词自身的值

– 标识符token、常数sum

– 关键字、运算符、界符token

三、 实验方法、步骤及结果测试

#include <stdio.h>
 #include <ctype.h>
 #include <malloc.h>
 #include <stdlib.h>
 #include <string.h>
 #define NULL 0
 FILE *fp;
   char cbuffer;
   char  *key[32]={"if","else","for","break","continue","int","float","double","auto","case","char","const","default","do","enum","long","extern","goto","register","return","short","signed","sizeof","static","struct","switch","typedef","union","unsigned","void","volatile","while"};
   char *border[8]={",",";","{","}","(",")","[","]"};
   char *arithmetic[4]={"+","-","*","/"};
   char *relation[6]={"<","<=","=",">",">=","<>"};
   char *consts[20]; char *label[20];
   int constnum=0,labelnum=0;
   int search(char searchchar[],int wordtype)
{
   int i=0;
   switch(wordtype)
{
   case 1:for(i=0;i<=31;i++)
{
   if (strcmp(key[i],searchchar)==0)
   return(i+1);
}
   return 0;
   case 2:
{  for (i=0;i<=7;i++)
{
   if (strcmp(border[i],searchchar)==0)
   return(i+1);
}
      return(0);
}
   case 3:
{
   for (i=0;i<=3;i++)
{
   if (strcmp(arithmetic[i],searchchar)==0)
{
   return(i+1);
}
}
   return(0);
}
   case 4:
{
   for (i=0;i<=5;i++)
   if (strcmp(relation[i],searchchar)==0)
    return(i+1);
   return(0);
 }
   case 5:
{
   for (i=0;i<=constnum;i++)
{
   if(consts[i] && (strcmp(consts[i],searchchar)==0))
    return(i+1);
    }
   consts[i-1]=(char *)malloc(sizeof(searchchar));
    strcpy(consts[i-1],searchchar);
    constnum++;
   return(i);
   }
 case 6:
   {
  for(i=0;i<=labelnum;i++)
    if(label[i] && (strcmp(label[i],searchchar)==0))
     return(i+1);
    label[i-1]=(char *)malloc(sizeof(searchchar));
  strcpy(label[i-1],searchchar);
   labelnum++;
  return(i);
   }
default:
return 0;
  }
 }
 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-1);
   printf("(1,  \"%s\")\n",alphatp);
  else
 {
 search(alphatp,6);
 //  printf("%s (6,%d)\n",alphatp,atype-1);
   printf("(2,  \"%s\")\n",alphatp);
  }
  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‘;
 search(digittp,5);
 // printf("%s (5,%d)\n",digittp,dtype-1);
 printf("(3,  \"%s\")\n",digittp);  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);
 printf("(4,  \"%s\")\n",othertp);
  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);
   printf("(4,  \"%s\")\n",othertp);
   goto out;
  }
 else
   othertp[1]=‘\0‘;
//  printf("%s (4,%d)\n",othertp,otype-1);
  printf("(4,  \"%s\")\n",othertp);
   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);
     printf("(5,  \"%s\")\n",othertp);
  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("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();
 }
}  

#inlclude<stdio.h>
 int main()
 {
     int d,a,c; a=10;
     c=a+b;
     printf("%d%d",a,b);;
     return 0;
 }

四.运行结果及分析