111.c

本程序是利用c编写的词法分析器

#include <stdio.h>
#include <string.h>
#include <process.h>
#define MAX 50
void main()
{
FILE *in,*out;/*存放输入字符串和输出单词串的文件*/
char arr[MAX];/*arr数组存放单词符号*/
int ch;
char currentchar;/*currentchar存放当前输入字符*/
int i=0;/*arr数组的一个指针*/
/*以读方式打开输入文件*/
if((in=fopen("infile.txt","r"))==NULL)
{
 printf("can not open file\n");
 exit(0);
}
/*以写方式打开输出文件*/
if((out=fopen("outfile.txt","w"))==NULL)
{
 printf("cannout open outfile\n");
    exit(1);
}
//去掉开头空格
currentchar=fgetc(in);
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}



while(currentchar!='@')
{
/*常数部分判断*/
if((currentchar>='a'&&currentchar<='z')||(currentchar>='A'&&currentchar<='Z')
   ||(currentchar>='0'&&currentchar<='9')||currentchar=='('||currentchar==')'
   ||currentchar=='{'||currentchar=='}'||currentchar=='>'||currentchar=='<'
   ||currentchar==';'||currentchar==':'||currentchar=='+'||currentchar=='-'
   ||currentchar=='*'||currentchar=='/'||currentchar=='='||currentchar=='!'
   ||currentchar=='&'||(ch=currentchar)=='\n'||currentchar==' '||currentchar=='['
   ||currentchar==']')
{
i=0;//清空arr字符数组
if(currentchar>='0'&&currentchar<='9')
{
 arr[i++]=currentchar;
    currentchar=fgetc(in);//再读入下一个字符
    while(currentchar>='0'&&currentchar<='9')
 {
    arr[i++]=currentchar;
    currentchar=fgetc(in);
 }
    if(currentchar!='.')//如果当前读入的符号不为小数点，则常数读完毕，输出此常数
 {
    arr[i++]='\0';
    fprintf(out,"%s%d,%c%s%c%s\n","(",15,'"',arr,'"',")");//格式化输出到目标文件，15代表种别码， arr为内码值，规定用数字本身代表
 }
    else//当前字符为小数点则继续向下读入
 {
    arr[i++]=currentchar;
    currentchar=fgetc(in);
    while(currentchar>='0'&&currentchar<='9')
 {
    arr[i++]=currentchar;
    currentchar=fgetc(in);
 }
    arr[i++]='\0';
    fprintf(out,"%s%d,%c%s%c%s\n","(",15,'"',arr,'"',")");
 }
    while(currentchar==' ')
 { 
 currentchar=fgetc(in);
 }
}
/*判断标识符和关键字部分*/
if((currentchar>='a'&&currentchar<='z')||(currentchar>='A'&&currentchar<='Z'))
{
i=0;//清空arr字符数组
    while((currentchar>='a'&&currentchar<='z')||(currentchar>='0'&&currentchar<='9')||(currentchar>='A'&&currentchar<='Z'))
 {
    arr[i++]=currentchar;
    currentchar=fgetc(in);
 }
//把字符数组arr和关键字表比较，判断单词串是关键字还是标识符
    arr[i++]='\0';
    if(strcmp(arr,"if")==0)
    fprintf(out,"%s%d,%c%s%c%s\n","(",0,'"',arr,'"',")");
    else if(strcmp(arr,"else")==0)
    fprintf(out,"%s%d,%c%s%c%s\n","(",1,'"',arr,'"',")");
    else if(strcmp(arr,"while")==0)
    fprintf(out,"%s%d,%c%s%c%s\n","(",2,'"',arr,'"',")");
    else if(strcmp(arr,"do")==0)
    fprintf(out,"%s%d,%c%s%c%s\n","(",3,'"',arr,'"',")");
 else
 fprintf(out,"%s%d,%c%s%c%s\n","(",14,'"',arr,'"',")");
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
//判断标识符包括：+, -, *, /, (, ), {, }, <, >, ;, :, !=, >=, <=, ==, =.
if(currentchar=='+')
{
    fprintf(out,"%s%d,%c%c%c%s\n","(",9,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar=='-')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",10,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar=='*')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",11,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar=='/')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",12,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar=='=')
{
 i=0;
 arr[i++]=currentchar;
 currentchar=fgetc(in);
 if(currentchar=='=')
 {
  arr[i++]=currentchar;
  arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",13,'"',arr,'"',")");
     currentchar=fgetc(in);
 }
 else
 { arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",17,'"',arr,'"',")");
    }
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar==';')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",4,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar=='{')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",5,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar=='}')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",6,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar=='[')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",20,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar==']')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",21,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar=='(')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",7,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar==')')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",8,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar==':')
{
 i=0;
 arr[i++]=currentchar;
 currentchar=fgetc(in);
 if(currentchar==':')
 {
  arr[i++]=currentchar;
  arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",18,'"',arr,'"',")");
     currentchar=fgetc(in);
 }
 else
 { arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",16,'"',arr,'"',")");
    }
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar=='>')
{
 i=0;
 arr[i++]=currentchar;
 currentchar=fgetc(in);
 if(currentchar=='=')
 {
  arr[i++]=currentchar;
  arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",13,'"',arr,'"',")");
     currentchar=fgetc(in);
 }
 else
 { arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",13,'"',arr,'"',")");
    }
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar=='<')
{
 i=0;
 arr[i++]=currentchar;
 currentchar=fgetc(in);
 if(currentchar=='=')
 {
  arr[i++]=currentchar;
  arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",13,'"',arr,'"',")");
     currentchar=fgetc(in);
 }
 else
 { arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",13,'"',arr,'"',")");
    }
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar=='!')
{
 i=0;
 arr[i++]=currentchar;
 currentchar=fgetc(in);
 if(currentchar=='=')
 {
  arr[i++]=currentchar;
  arr[i++]='\0';
  fprintf(out,"%s%d,%c%s%c%s\n","(",13,'"',arr,'"',")");
     currentchar=fgetc(in);
 }
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
if(currentchar=='&')
{
 fprintf(out,"%s%d,%c%c%c%s\n","(",19,'"',currentchar,'"',")");
    currentchar=fgetc(in);
}
while(currentchar==' ')
{ 
 currentchar=fgetc(in);
}
while((ch=currentchar)=='\n')
{
 currentchar=fgetc(in);
}
 while(currentchar==' ')
{
 currentchar=fgetc(in);
}
}
else
{
 fprintf(out,"%s,%c%c%c\n","error",'"',currentchar,'"');
    currentchar=fgetc(in);
}

}//结束开头while语句
/*关闭文件退出*/
fclose(in);
fclose(out);
}