readme.txt

这是一个能够判断单词结构的词法分析器小程序,它能够分析单词符号传递的语法语义.

主要的代码如下（这里给出的是命令行代码，稍加修改就可以做成源码中国演示图片的界面了）

　
#include
#include
#include
#include

#define  MAX 18   //分析表的最大容量
#define  MAXBUF 255
char  ch =' ';   // 存放读入当前的输入字符
int lineno;

struct reserve   //关键字
{
 char lexptr[MAXBUF];
 int token;
};

struct reserve symtable[MAX];
char * str[]={"program","input","output","begin","end","var","integer","real","for","to","if","then","else","do","while","write","array","proceure" };


void init()     //对符号表进行初始化
{
 for( int j=0; j<18; j++)
 { 
  strcpy(symtable[j].lexptr,str[j]);
  symtable[j].token=j+3;
 }
}
 

int search(char *temp)
{
 for(int i=0; i {
  if(!strcmp(symtable[i].lexptr ,temp))
  {
   return  symtable[i].token;
  }
 }
 return 0;
}     

 

void analyse(FILE *fpin,FILE *fpout)    //分析程序
{
 char arr[MAXBUF];
 int i=0;
 int j=0;
 
 while((ch=fgetc(fpin))!=EOF)    //读入字符判断，空格、字母、数字、界符
 {
  if(ch==' '||ch=='\t')
  {
   
  }
  else if(ch=='\n')    //如果是换行符，则行号加1
  {  
   lineno++;
  }
  else if(isdigit(ch))   //如果是数字
  { 
   while(isdigit(ch))   //判断和读取数字
   { 
    arr[j]=ch;
    j++;
    ch=fgetc(fpin);
   } 
   arr[j]='\0';
   j=0;
   fseek(fpin,-1L,SEEK_CUR);
   fprintf(fpout,"%s\t%d\n",arr,2) ;
  }
  else if (isalpha(ch))  //如果是字母
  {
   while(isalpha(ch)||isdigit(ch))
   {
    arr[j]=ch;
    j++;
    ch=fgetc(fpin);
   }
   fseek(fpin,-1L,SEEK_CUR);
   arr[j]='\0';
   j=0;
   if (search(arr)) //如果是关键字
   {
    fprintf(fpout,"%s\t%d\n",arr,search(arr));
   }
   else  
    fprintf(fpout,"%s\t%d\n",arr,1); //普通标志符
  }
  else if(ch==':')  
  {
   ch=fgetc(fpin);
   if(ch=='=') 
   {
    fprintf(fpout,"%s\t%d\n",":=",29);    //如果是 :=
   }
   else
   {
    fprintf(fpout,"%s\t%d\n",":",30);   //如果是 :
    fseek(fpin,-1L,SEEK_CUR);
   }
  }
  else if (ch=='>')
  {
   ch=fgetc(fpin);
   if(ch=='=')    //如果是 >=
   {
    fprintf(fpout,"%s\t%d\n",">=",32);
   }
   else
   {
    fprintf(fpout,"%s\t%d\n",">",31);  //如果是 >
    fseek(fpin,-1L,SEEK_CUR);
   }
  }
  else if(ch=='<')
  { 
   ch=fgetc(fpin);
   if(ch=='>')
   {
    fprintf(fpout,"%s\t%d\n","<>",35);  // 如果是 <>
   }
   else if(ch=='=')
   {
    fprintf(fpout,"%s\t%d\n","<=",34);   //如果是 <=
   }
   else 
   {
    fprintf(fpout,"%s\t%d\n","<",33);   //如果是 <
    fseek(fpin,-1L,SEEK_CUR);
   }
  }
  else if(ch=='/')
  { 
   ch=fgetc(fpin);
   if(ch=='*')
   {
    ch=fgetc(fpin);
s:
    while(ch!='*')
    {
     ch=fgetc(fpin);
    }
    while(ch=='*')
    {
     ch=fgetc(fpin);
     while(ch!='/')
     {
      goto s;   //如果是注释 /*  */
     }
    }
   }
   else if(ch=='/')
   {
    ch=fgetc(fpin);
    while(ch!='\n')
    {
     ch=fgetc(fpin);   //如果是注释 //
    }
   }
   else 
   {  
    fprintf(fpout,"%s\t%d\n","/",24);
    fseek(fpin,-1L,SEEK_CUR);
   }
  }
  else if(ch=='+')
  {
   fprintf(fpout,"%s\t%d\n","+",21);
  }
  else if(ch=='-')
  {
   fprintf(fpout,"%s\t%d\n","-",22);
  }
  else if(ch=='*')
  {
   fprintf(fpout,"%s\t%d\n","*",23);
  }
  else if(ch=='(')
  {
   fprintf(fpout,"%s\t%d\n","(",25);
  }
  else if(ch==')')
  {
   fprintf(fpout,"%s\t%d\n",")",26);
  }
  else if(ch=='[')
  {
   fprintf(fpout,"%s\t%d\n","[",27);
  }
  else if(ch==']')
  {
   fprintf(fpout,"%s\t%d\n","]",28);
  }
  else if(ch=='.')
  {
   fprintf(fpout,"%s\t%d\n",".",39);
  }
  else if(ch==';')
  {
   fprintf(fpout,"%s\t%d\n",";",36);
  }
  else if(ch=='=')
  {
   fprintf(fpout,"%s\t%d\n","=",38);
  }
  else if(ch==',')
  {
   fprintf(fpout,"%s\t%d\n",",",40);
  }
  else fprintf(fpout,"无法识别的字符 %c\n",ch)  ;
   }
} 


void main()
{
 printf("***************************词法分析器*************************\n\n\n");
 printf("直接输入源代码请按1，从文件中读入源代码请按2 \n") ;
 
 
 char filenamein[10];
 char filenameout[10];
   
 printf("请输入源文件名：\n");
 scanf("%s",filenamein);
 printf("请输入保存词法分析结果的文件名：\n");
 scanf("%s",filenameout);
 FILE* fpin=fopen(filenamein,"r");
 FILE* fpout=fopen(filenameout,"w");
 init();
 analyse(fpin,fpout);
 fclose(fpin);
 fclose(fpout);
 
 
 getch();
}